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1.
Org Biomol Chem ; 21(24): 5021-5032, 2023 Jun 21.
Article in English | MEDLINE | ID: mdl-37260347

ABSTRACT

Lewis base dependent (3 + 3) annulation of δ-acetoxy allenoates with benzofuranone, pyrazolone, and Boc-protected oxindole is reported. In the presence of catalytic DBU, oxindole, benzofuranone, and pyrazolone undergo (3 + 3) annulation with δ-acetoxy allenoates via 6-exo-dig cyclisation at room temperature (25 °C) to afford fused pyran scaffolds. On the other hand, by employing catalytic DMAP, the reaction between N-Boc-oxindole and δ-acetoxy allenoates goes through 6-endo-dig cyclisation, leading to distinct dihydropyrans that contain an exocyclic double bond; similar products were also obtained by using benzofuranone and pyrazolone.

2.
Org Biomol Chem ; 21(1): 195-208, 2022 Dec 21.
Article in English | MEDLINE | ID: mdl-36484437

ABSTRACT

Ru(II)-catalysed oxidative (4 + 2) annulation of chromene and coumarin-3-carboxylic acids with alkynes/propargylic alcohols via sp2 C-H bond activation is reported. While the reaction with alkynes affords highly substituted pyrano-chromones in good to excellent yields, the use of methyl-tethered propargylic alcohols in place of alkynes leads to novel Ru(0)-metal complexes in moderate to good yields; these complexes were stable in MeCO2H/O2. The generality of the reaction with alkynes is illustrated in the case of both symmetrical and unsymmetrical internal alkynes with excellent regioselectivity in the case of unsymmetrical alkynes.

3.
Org Biomol Chem ; 20(46): 9148-9160, 2022 11 30.
Article in English | MEDLINE | ID: mdl-36346226

ABSTRACT

Palladium-catalysed and base-dependent intra-molecular ipso-substitution and cyclisation strategies involving N-indolyl-substituted aryl-sulfonamides for the rapid construction of 2-aryl indole and indole-fused six-membered sultams are described. The Pd(OAc)2/Ph3P/Et3N combination delivers indolyl C2 arylated motifs via C(2)-N bond cleavage followed by C-C bond formation. In sharp contrast to this, the Pd(OAc)2/Ph3P/K2CO3 combination induced intramolecular-Heck cross-coupling affords polycyclic sultams exclusively. Thus, this strategy is completely additive-dependent. It also shows a broad substrate scope and delivers the corresponding products in good to high yields.


Subject(s)
Naphthalenesulfonates , Palladium , Catalysis , Palladium/chemistry , Indoles/chemistry
4.
J Org Chem ; 86(17): 11583-11598, 2021 Sep 03.
Article in English | MEDLINE | ID: mdl-34343010

ABSTRACT

The reactivity of 2-sulfonamidoindoles with acetoxy allenoates under phosphine catalysis depends on the disposition of the acetoxy (OAc) group on the allenoate. In the temperature-controlled [3 + 3] annulations, δ-acetoxy allenoates afforded dihydrocarboline and carboline scaffolds with carbon-nitrogen nucleophilic 2-sulfonamidoindoles, in which allenoate serves as a ß-, γ-, and δ-carbon donor. At room temperature (25 °C), dihydro-α-carboline motifs were obtained exclusively through Michael addition, 1,4-proton shift, isomerization, 1,2-proton transfer, phosphine elimination, and aza-Michael addition. The higher temperature (80 °C) cascade protocol using Ph3P-Cs2CO3 combination involves addition-elimination, aza-Claisen rearrangement, tosyl migration, and aromatization as key steps to give α-carbolines containing tosyl functionality at the γ-carbon. In contrast, with ß'-acetoxy allenoate, 2-sulfonamidoindole acts only as a carbo-nucleophile in (p-tolyl)3P-directed [4 + 1] spiro-annulation, leading to five-membered spiro-carbocyclic motifs essentially as single diastereomers (dr >20:1) via chemoselective carbo-annulation.

5.
Org Biomol Chem ; 19(31): 6871-6882, 2021 08 11.
Article in English | MEDLINE | ID: mdl-34323909

ABSTRACT

An efficient and straightforward Pd-catalysed synthesis of diversely substituted sultams utilising ynamides and boronic acids is disclosed; toluene was found to be the most suitable solvent for this transformation. This strategy has been successfully applied to generate dihydrobenzo[d]isothiazole 1,1-dioxides and dihydro-2H-benzo[e][1,2]thiazine 1,1-dioxides. The advantages of this protocol are good functional group tolerance, broad substrate scope, high-yielding reaction and low catalyst loading to access benzofused sultams with five-/six-membered rings. The synthetic utility has been demonstrated by a gram-scale synthesis. A plausible catalytic cycle involving carbopalladation has been proposed for this transformation.

6.
Org Biomol Chem ; 17(28): 6880-6894, 2019 07 17.
Article in English | MEDLINE | ID: mdl-31270513

ABSTRACT

An efficient Cu(i)-catalysed cyclisation reaction of 2-iodobenzene sulfonamides with aryl-isothiocyanates and isocyanates that affords functionalised benzodithiazines and benzothiadiazinones, respectively, has been developed. Thus, in the reaction with aryl isothiocyanates (Ar-N[double bond, length as m-dash]C[double bond, length as m-dash]S), the C[double bond, length as m-dash]S moiety participates in the cyclisation leading to a dithiazine. By contrast, in the case of aryl isocyanates (Ar-N[double bond, length as m-dash]C[double bond, length as m-dash]O), the N[double bond, length as m-dash]C part is involved in the cyclisation and a thiadiazinone is obtained. Analogous reactions of isothiocyanates with N-tosyl-2-iodo-anilines and 2-iodo-benzyl sulfonamides afford (benzothiazin-2-ylidene)anilines and (benzothiazol-2-ylidene)anilines, respectively. Probable mechanistic pathways are briefly discussed.

7.
Org Biomol Chem ; 17(23): 5736-5748, 2019 Jun 12.
Article in English | MEDLINE | ID: mdl-31120467

ABSTRACT

Multifunctional γ-azido/γ-fluoro-ß-iodo-vinyl phosphine oxides/phosphonates/esters/sulfone were synthesised by iodination followed by azidation/fluorination of phosphorus-based allenes or allenoates (allenyl esters) or a sulphur based allene. Surprisingly, the reaction of (γ,ß)-diiodo-vinyl-phosphonate with TBAF [n-Bu4NF] led to the corresponding allenylphosphonate; in contrast, the use of CsF in a similar reaction led to novel γ-diiodo-allenylphosphonate along with the corresponding non-halogenated allenylphosphonate. The combination AgF2/CuBr could be used to obtain the γ-fluoro-ß-iodo-vinyl phosphine oxides and related phosphorus-free γ-fluoro-ß-iodo-vinyl esters. In many cases, IO halogen to oxygen non-covalent bonding interactions ('halogen bonding') involving the phosphoryl (P[double bond, length as m-dash]O) oxygen, as evidenced by single crystal X-ray crystallography, are also observed.

8.
Org Biomol Chem ; 17(12): 3275-3284, 2019 03 20.
Article in English | MEDLINE | ID: mdl-30848275

ABSTRACT

Gold-catalysed intramolecular reaction of unprotected/protected 3-dienyl indoles leads to the formation of functionalised terphenylamines with high efficiency; this reaction can also be accomplished in one pot by starting with 2-arylindole and propargylic alcohols. This reaction occurs via 3-dienyl indoles and proceeds likely by gold-catalysed cascade cyclisation, aromatisation and fragmentation of the indole heterocyclic moiety. We have also found that PTSA can work well giving comparable yields, but at least one mole equivalent of PTSA is required. On the other hand, 3-indenylindoles have been synthesised from indole-2-carboxylates (2-carboxyindoles) and propargylic alcohols through Brønsted acid mediation. Many of these indenylindoles exhibit isomerism (probably diastereomers) in the solution state (1H NMR). Two examples of indolo-indenyl acetates have been prepared by reacting the above terphenylanilines with PhI(OAc)2. Key products are characterised by X-ray crystallography.

9.
Angew Chem Int Ed Engl ; 56(24): 6984-6988, 2017 06 06.
Article in English | MEDLINE | ID: mdl-28471083

ABSTRACT

Ethanol is shown to act as a hydrogenating agent for ynamides under palladium catalysis. This behavior is different from the normally expected reaction of ethanol addition to alkynes. The reaction shows stereoselectivity for E enamides, which is in contrast to reports using other hydrogenating sources. The method was also extended to ynamines. Alternatively, the use of ethanol and ammonium formate as the hydrogenating source gives Z enamides. The role of ethanol in hydrogenation was demonstrated by means deuterium labeling experiment.

10.
Org Biomol Chem ; 14(14): 3591-602, 2016 Apr 14.
Article in English | MEDLINE | ID: mdl-26976203

ABSTRACT

Reaction of N-Bz protected o-aminobenzaldehyde or acetophenone with allenylphosphonates in the presence of a simple base leads to quaternary carbon substituted phosphono-quinolines which undergo thermal rearrangement to O-phosphorylated quinolines. The present one-pot reaction involves intermolecular cyclisation, dehydration, and benzoyl group rearrangement followed by a novel phosphoryl group migration. The migration was less facile/not observed in the reactions using allenylphosphine oxides and sulphur based allenes wherein only substituted quinolines were obtained in good yields. X-ray structures have been determined for the key products.

11.
J Org Chem ; 81(4): 1425-33, 2016 Feb 19.
Article in English | MEDLINE | ID: mdl-26771256

ABSTRACT

[Au]-catalyzed [3 + 3] cycloaddition reaction of enynones/enynals with azides, which allows the efficient regioselective synthesis of highly fused furo[3,4-d][1,2,3]triazines in good-to-excellent yields under mild conditions, has been developed. The synthetic utility of furanotriazines was exploited by oxidation with cerium ammonium nitrate (CAN) affording highly functionalized dihydrotriazines. Both furo[3,4-d][1,2,3]triazines and dihydrotriazines exhibit good fluorescence activity.

12.
Org Biomol Chem ; 13(39): 10060-71, 2015 Oct 21.
Article in English | MEDLINE | ID: mdl-26335651

ABSTRACT

One-pot synthesis of highly substituted norbornadienes/norbornenes via gold-catalysed dehydrative cyclisation of alkynyldienols, followed by intermolecular [4 + 2] cycloaddition of in situ generated cyclopentadiene and activated alkynes/alkenes is described. The precursors, alkynyldienols, are obtained via sequential Sonogashira cross-coupling of 3-bromoenals, alkyne addition and reduction. Yields of the enynals and multisubstituted norbornadienes in all the cases are good to excellent.

13.
Chem Commun (Camb) ; 51(60): 12008-11, 2015 Aug 04.
Article in English | MEDLINE | ID: mdl-26120942

ABSTRACT

Palladium catalysed-reaction of indole carboxylic acids with nitriles in the presence of Ag2CO3 proceeds via decarboxylative dual C-H activation leading to the nitrile insertion products, triazaindeno-fluorenes (indolocarbolines); in the absence of nitrile, diindolocarbazoles (heptacyclic triindoles or triazatruxenes) are formed.

14.
Org Lett ; 17(12): 2996-9, 2015 Jun 19.
Article in English | MEDLINE | ID: mdl-26052834

ABSTRACT

A novel and efficient [Cu]-catalyzed one-pot regio- and stereospecific synthesis of benzo[1,4,2]dithiazine 1,1-dioxides and benzo[1,4,2]thiaselenazine 1,1-dioxides by cyclization of functionalized ynamides with elemental sulfur/selenium has been developed. Its generality is elegantly illustrated by extension to benzodithiazepines and benzothiaselenazepines. Involvement of water in the reaction is demonstrated by the incorporation of (2)D at the olefinic site by using D2O in place of water. Selective oxidation at sulfur in benzo[1,4,2]dithiazine 1,1-dioxide by using mCPBA as the oxidizing agent is also described.

15.
Org Biomol Chem ; 11(42): 7350-60, 2013 Nov 14.
Article in English | MEDLINE | ID: mdl-24057008

ABSTRACT

Dual copper catalysis, involving two different reactions, click (alkyne-azide) and carbon-oxygen bond formation (aryl iodide-secondary alcohol) in a single step, is reported. Synthesis of novel benzodioxines (benzodioxanes), benzoxazines, benzoxathiines and benzodioxepines, which feature benzo-condensed six or seven membered rings containing two hetero-atoms attached to a 1,2,3-triazole, is described. As an extension, such compounds were also synthesised by ring opening of epoxide and cyclisation using Cu(I). All the key products have been characterized by single crystal X-ray crystallography.


Subject(s)
Benzoxazines/chemistry , Benzoxepins/chemistry , Click Chemistry , Copper/chemistry , Dioxins/chemistry , Triazoles/chemistry , Carbon/chemistry , Catalysis , Oxygen/chemistry
16.
Org Biomol Chem ; 10(40): 8113-8, 2012 Oct 28.
Article in English | MEDLINE | ID: mdl-22951942

ABSTRACT

An efficient base catalysed approach to the synthesis of thiochromans/chromenes from allenylphosphonates (and an allenoate) and substrates having SH/OH and CHO groups at appropriate positions has been developed. Several azo-linked chromenes that are bright red pigments are also synthesized. This methodology involves the domino reactions of Michael addition and subsequent cyclisation by intramolecular aldol reaction.


Subject(s)
Alkadienes/chemistry , Azo Compounds/chemical synthesis , Chromans/chemical synthesis , Organophosphates/chemistry , Sulfhydryl Compounds/chemical synthesis , Azo Compounds/chemistry , Catalysis , Chromans/chemistry , Magnetic Resonance Spectroscopy , Models, Molecular , Molecular Structure , Sulfhydryl Compounds/chemistry
17.
J Org Chem ; 77(19): 8712-22, 2012 Oct 05.
Article in English | MEDLINE | ID: mdl-22963608

ABSTRACT

Thermolysis of phosphorus-based vinyl azides under solvent- and catalyst-free conditions furnished a new route for 1,4-pyrazines. A simple one-pot, Mn(III)-catalyzed photochemical route has been developed for multisubstituted pyrroles starting from allenes and 1,3-dicarbonyls via in situ-generated vinyl azides. The utility of new phosphorus-based pyrroles is also demonstrated in the Horner reaction. The structures of key products are unequivocally confirmed by X-ray crystallography.


Subject(s)
Azides/chemistry , Manganese/chemistry , Pyrroles/chemistry , Vinyl Compounds/chemistry , Catalysis , Crystallography, X-Ray , Molecular Structure , Photochemical Processes , Pyrazines
18.
J Org Chem ; 77(12): 5345-56, 2012 Jun 15.
Article in English | MEDLINE | ID: mdl-22651243

ABSTRACT

Utilizing internally available functional groups, a simple protocol for the efficient synthesis of phosphorus-based indenes, indenones, benzofurans, and isochromenes via intramolecular cyclization of allene intermediates/precursors is generated; the latter intermediates/precursors are conveniently obtained through aldehyde-, alkylidene-, and hydroxyl-functionalized propargyl alcohols and P(III)-Cl precursors. The structures of key products have been unequivocally confirmed by X-ray crystallography.


Subject(s)
Benzofurans/chemistry , Benzofurans/chemical synthesis , Benzopyrans/chemistry , Benzopyrans/chemical synthesis , Indenes/chemistry , Indenes/chemical synthesis , Organophosphorus Compounds/chemistry , Organophosphorus Compounds/chemical synthesis , Phosphines/chemistry , Catalysis , Cyclization , Molecular Structure , Stereoisomerism
19.
Dalton Trans ; 41(3): 1004-12, 2012 Jan 21.
Article in English | MEDLINE | ID: mdl-22105914

ABSTRACT

The reaction of triphenylbismuth [BiPh(3)] with several heterocyclic carboxylic acids was explored. Seven crystalline compounds, [PhBi(2-O(2)C-3-(OH)C(5)H(3)N)(2)(2-O(2)C-3-(OH)C(5)H(3)NH)] (5), [(Bi(2-O(2)C-3-(OH)C(5)H(3)N)(4))(C(5)H(5)NH)(C(5)H(5)N)] (7), [PhBi(2-O(2)C-C(4)H(3)N(2))(2)(2-O(2)C-C(4)H(4)N(2))·H(2)O] (8), [PhBi(2-O(2)C-C(9)H(6)N)(2)·H(2)O] (9), [Ph(2)Bi(O(2)C-C(4)H(3)O)] (10), [Ph(2)Bi(O(2)C-C(4)H(3)S)] (11) and [PhBi(O(2)C-C(4)H(3)S)(2)](2) (12), were prepared by simple reactions using BiPh(3) and the corresponding acids, 3-hydroxypicolinic acid, pyrazine-2-carboxylic acid, quinoline-2-carboxylic (quinaldic) acid, furan-2-carboxylic acid and thiophene-2-carboxylic acid. Compound 5 primarily exhibits a coordination number of six with pentagonal pyramidal geometry at bismuth, but an additional weak Bi···O interaction in the direction of the lone pair of electrons is present. This feature leads to a weakly bound dimer. The use of pyridine as the solvent in a similar reaction, however, led to 7, in which all of the Bi-Ph bonds are cleaved. In this compound, bismuth exhibits a coordination number of eight and distorted dodecahedral geometry. In compound 8, the geometry around bismuth is primarily a pentagonal pyramid, however, clear-cut but weak secondary Bi···N interactions leading to a dimeric formulation are discernible in the structure. The quinaldate compound 9 exhibits a lower formal coordination number of five for bismuth, with square pyramidal geometry, but again two secondary Bi···O interactions for each bismuth in the direction of the lone pair lead to a dimer. A similar secondary Bi···O interaction involving furan oxygen is present in the furoate compound 10, which is a polymeric chain (one dimensional coordination polymer). Although the thiophene carboxylate 11 is also a polymeric chain, no Bi···S interactions are present. Unlike the previously reported tetrameric biscarboxylate [PhBi(2-O(2)C-C(5)H(3)N)(2)](4), the thiophene carboxylate [PhBi(O(2)C-C(4)H(3)S)(2)](2) (12) is a dimer considering only primary interactions. However, these dimers are arranged in such a way that there are secondary Bi···S interactions in the structure in the expected direction of the lone pair of electrons on bismuth. Thus, these studies suggest that the stereochemical activity (or inactivity) of the bismuth lone pair of electrons need to be judged more cautiously. TGA studies are consistent with the presence of Bi-Ph groups in all of the compounds, except 7, as indicated by their formulae.


Subject(s)
Carboxylic Acids/chemistry , Organometallic Compounds/chemistry , Terphenyl Compounds/chemistry , Bismuth/chemistry , Crystallography, X-Ray , Molecular Structure
20.
Carbohydr Res ; 342(9): 1182-8, 2007 Jul 02.
Article in English | MEDLINE | ID: mdl-17379195

ABSTRACT

Treatment of the phosphoramidite [myo-C(6)H(6)-2-[OC(O)Ph]-1,3,5-(O(3)CH)-4,6-(O(2)P-NH-i-Pr)] with o-chloranil affords the first example of inositol-based pentacoordinate phosphorane [myo-C(6)H(6)-2-[OC(O)Ph]-1,3,5-(O(3)CH)-4,6-(O(2)P-NH-i-Pr)(1,2-O(2)C(6)Cl(4))] (9) (X-ray structure) with a trigonal bipyramidal geometry at phosphorus. The six-membered 1,3,2-dioxaphosphorinane ring with the inositol residue has an unusual boat conformation in 9 which is quite different from that found in unrestrained rings investigated before, but is similar to that of its P(III) chloro precursor [myo-C(6)H(6)-2-[OC(O)Ph]-1,3,5-(O(3)CH)-4,6-(O(2)PCl)] (X-ray structure). Also, a convenient and chromatography-free procedure for the protected myo-inositol derivative [myo-C(6)H(6)-2-[OC(O)Ph]-1,3,5-(O(3)CH)-4,6-(OH)(2)] is reported.


Subject(s)
Inositol/chemistry , Phosphoranes/chemistry , Phosphoranes/chemical synthesis , Carbohydrate Conformation , Chloranil/analogs & derivatives , Chloranil/chemistry , Molecular Conformation , Molecular Structure , Stereoisomerism
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