PS-BEMP as a basic catalyst for the phospha-Michael addition to electron-poor alkenes.

PS-BEMP was used as a heterogeneous catalyst for the phospha-Michael addition of phosphorus nucleophiles to a variety of electron-poor alkenes. The addition reactions were generally performed with equimolar amounts of reagents under solvent free conditions. The protocol proved to be very efficient for the addition to aromatic, non-aromatic and cyclic ketones, giving good yields (78-85%) in all cases. The protocol was also extended with good results to α,ß-unsaturated esters and nitriles. This demonstrates that PS-BEMP is a good catalyst for the phospha-Michael addition to electron-poor alkenes.

A catalytic approach to the metal-free reaction of epoxides with ketene silyl acetals for accessing γ-lactones.

The first catalytic approach to the nucleophilic addition of silyl ketene acetals 2 to epoxides 1 is reported. The defined protocol is metal-free using tetrabutylammonioum fluoride as the catalyst. It works in a very efficient manner under solvent-free conditions (SolFC) allowing γ-lactones 3 to be directly obtained with high regioselectivities and yields.

E-Factor minimized hydrophosphonylation of aldehydes catalyzed by polystyryl-BEMP under solvent-free conditions.

An efficient protocol for the hydrophosphonylation of aromatic and aliphatic aldehydes catalyzed by PS-BEMP under solvent-free conditions (SolFC) has been reported. Addition reactions were performed by using equimolar amounts of reagents and the resulting α-hydroxyphosphonates were isolated with simple workup procedures. A large scale protocol for the preparation of a representative α-hydroxyphosphonate 3a has been also set up using a flow reactor.

A protocol for accessing the ß-azidation of α,ß-unsaturated carboxylic acids.

This contribution reports the preparation and use of a new immobilized catalyst, PS-DABCOF (9), which has been specifically designed to access for the first time the efficient ß-azidation of α,ß-unsaturated carboxylic acids.

Sc(III)-catalyzed enantioselective addition of thiols to α,ß-unsaturated ketones in neutral water.

This report concerns Lewis acid catalyzed enantioselective sulfa-Michael addition in neutral water by using a very efficient Sc(OTf)(3)/bipyridine 1 catalytic system. It is noteworthy that the protocol presented employs water as a reaction medium and allows us to obtain very high stereoselectivity and satisfactory yields for ß-keto sulphides deriving from aliphatic thiols. The recovery and reuse of both the aqueous medium and the catalytic system is also reported.

High pressure Diels-Alder approach to hydroxy-substituted 6a-cyano-tetrahydro-6H-benzo[c]chromen-6-ones: a route to delta(6)-cis-cannabidiol.

Diels-Alder cycloaddition reactions of 3-cyanocoumarin, hydroxy-substituted 3-cyanocoumarins and mesyl-substituted 3-cyano-coumarins with methyl-1,3-butadienes carried out under high pressure (11 kbar) are reported. Activation by high pressure allows these reactions to proceed satisfactorily under mild conditions to produce 6a-cyano-hydroxy- and 6a-cyano-mesyl-tetrahydro-6H-benzo[c]chromen-6-ones in moderate to excellent yield. The synthesis of cis-1-hydroxy-9-methyl-3-pentyl-6a,7,10,10a-tetrahydro-benzo[c]chromen-6-one as precursor of Delta(6)-3,4-cis-cannabidiol (Delta(6)-cis-CBD) and Delta(8)-cis-tetrahydrocannabinol (Delta(8)-cis-THC) is outlined.

Amberlite IRA900N3 as a new catalyst for the azidation of alpha,beta-unsaturated ketones under solvent-free conditions.

Amberlite IRA900N3 is an excellent organocatalyst for the azidation of alpha,beta-unsaturated ketones with trimethylsilyl azide under solvent-free conditions. By avoiding the use of metallic species and of the organic reaction medium, the procedure is a green tool for the preparation of beta-azido ketones under mild conditions with yields from good to excellent. The catalyst can be recovered and re-used with no loss of its efficiency.

Uncatalyzed and solvent-free multicomponent process for the synthesis of biphenyl-2-carbonitrile derivatives.

An innovative route to prepare a number of variously substituted new biphenyl derivatives is presented here. The protocol avoids the use of a catalyst, an organic solvent, and dry conditions. [reaction: see text]

[AlCl3 + 2THF]: a new and efficient catalytic system for Diels-Alder cycloaddition of alpha,beta-unsaturated carbonyl compounds under solvent-free conditions.

[AlCl(3) + 2THF] is a new catalytic system for the Diels-Alder cycloaddition under SFC and air atmosphere. By using equimolar amounts of reactants, this catalyst prevents the polymerization of the diene and allows the corresponding adducts to be isolated with high regio- and stereocontrol and in excellent yields. [reaction: see text]

Diels-Alder reactions of 3-substituted coumarins in water and under high-pressure condition. An uncatalyzed route to tetrahydro-6H-benzo[c]chromen-6-ones.

[reaction: see text] Diels-Alder reactions of 3-substituted coumarins 1a-g with methyl-1,3-butadienes 2a-c carried out in water alone and in CH2Cl2 under 9 kbar pressure are reported. In aqueous medium satisfactory results were obtained by operating at 150 degrees C, whereas under high pressure the cycloadditions were complete at 60-70 degrees C with excellent yields (85-95%). The reactions with isoprene (2b) always resulted in the exclusive formation of para cycloadducts, whereas with (E)-piperylene (2c) only ortho products were detected. The cycloaddition of 3-phenylsulfonylcoumarin (1a) with (E)-piperylene (2c) allowed the endo adduct to be obtained exclusively, whereas 3-carboxycoumarin (1b) reacted with 2c to give a mixture of the corresponding endo/exo adducts in a 58:42 ratio in water and in a 45:55 ratio under high-pressure condition.

InCl3-catalyzed regio- and stereoselective thiolysis of alpha,beta-epoxycarboxylic acids in water.

[reaction: see text] The thiolysis of alpha,beta-epoxycarboxylic acids 1a-e by thiols 2a,b is more efficient in water than in dichloromethane or SFC. At pH 9.0 phenylthiolate generally attacks the C-alpha carbon while at pH 4.0, and in the presence of InCl3 (10 mol %), the thiolysis is exclusively C-beta regioselective. In all cases, the processes are completely anti-diasteroselective, and the corresponding products 3, 4, and 5 have been isolated in good yields. Both water and catalysts have been recovered and reused.

Synthesis of 4-aryl-1H-1,2,3-triazoles through TBAF-catalyzed [3 + 2] cycloaddition of 2-aryl-1-nitroethenes with TMSN3 under solvent-free conditions.

TBAF-catalyzed [3 + 2] cycloaddition reactions of 2-aryl-1-cyano- or 2-aryl-1-carbethoxy-1-nitroethenes 1 with TMSN3 under SFC allow the corresponding 4-aryl-5-cyano- or 4-aryl-5-carbethoxy-1H-1,2,3-triazoles 2 to be prepared under mild reaction conditions and with good to excellent yields (70-90%). The proposed protocol does not require dried glassware or inert atmosphere.

One-pot synthesis of benzo[e]1,4-oxathiepin-5-ones under solvent-free condition via self-promoted thiolysis of 1,2-epoxides.

Under solvent-free conditions, thiosalicylic acid (2) efficiently self-promotes the thiolysis of 1,2-epoxides 1, anti-stereoselectively and generally totally beta-regioselectively. The resulting beta-hydroxysulfide products 3 have been obtained in very good yields. Benzo[e]1,4-oxathiepin-5-ones 4 have been easily prepared in a regio- and diasteroselective manner and in satisfactory yields under SFC by a one-pot protocol including nucleophilic ring opening of 1,2-epoxides 1 by thiosalicylic acid (2) and thermally induced lactonization of beta-hydroxy arylsulfides 3. Solvent-free condition and the absence of any catalyst make this procedure atom-economical and environmentally friendly.

Polystyryl-supported TBD as an efficient and reusable catalyst under solvent-free conditions.

Polystyryl supported-TBD (PSTBD) is an efficient and reusable heterogeneous basic catalyst under solvent-free conditions for a variety of organic transformations such as 1,2-epoxide ring-opening, aldol-type condensation and Michael addition.

Solvent-free Al(OTf)3-catalyzed aminolysis of 1,2-epoxides by 2-picolylamine: a key step in the synthesis of ionic liquids.

Beta-Amino alcohols N-2'-pyridylmethyl substituted 3 have been prepared in excellent yields under mild conditions by the first Lewis acid-catalyzed aminolysis of 1,2-epoxides 1 with the bihaptic amine 2-picolylamine (2) with use of 5 mol % of Al(OTf)(3) under solvent-free conditions. As a representative of a new class of ionic liquids, cis-5-[(4'-methylphenyl)sulfonyl]-1,2,3,4,4a,5,6,11a-octahydropyrido[1,2-a]quinoxalin-11-ium methanesulfonate (6) and its chloride derivative 7 have been synthesized under environmentally friendly conditions by the one-pot aminolysis of cyclohexene oxide (1a) with 2 and intramolecular cyclization of the resulting 2-[(pyridin-2'-yl)methylamino]cyclohexanol (3a).

TBAF-catalyzed synthesis of 5-substituted 1H-tetrazoles under solventless conditions.

Tetrabutylammonium fluoride (TBAF) is an efficient catalyst in the [3 + 2] cycloaddition reaction of organic nitriles 1 with trimethylsilyl azide (TMSN(3)) in solventless conditions. The corresponding 5-substituted 1H-tetrazoles 2 were obtained under mild conditions and in 80-97% yields.

NaOH-catalyzed thiolysis of alpha,beta-epoxyketones in water. A key step in the synthesis of target molecules starting from alpha,beta-unsaturated ketones.

NaOH (0.02-0.3 molar equiv) is an efficient catalyst for the thiolysis reactions of alpha,beta-epoxy ketones with alkyl and aryl thiols in water. Thiolysis of 3,4-epoxyheptan-2-one (1) with thiols 2a-d has been accomplished in mild conditions (30 degrees C and pH 6 or 9) with complete C-alpha-regioselectivity and anti-stereoselectivity, and the corresponding anti-beta-carbonyl-beta-hydroxysulfides 3a-d have been prepared in excellent yields (95-98%). Compounds 3a-d, depending on their nature and pH conditions, have undergone dehydration, C-3 epimerization reaction, and retroaldol condensation. Dehydration of anti-3a-d has been chemoselectively carried out by in situ acidic treatment at 70 degrees C, giving stereoselectively the related (Z)-vinyl sulfides 4 in 89-94% overall yields. Under NaOH-catalyzed thiolysis conditions, cyclic alpha,beta-epoxyketones 6-9 have shown C-alpha attack only and spontaneously dehydrated to furnish the corresponding vinyl sulfides in high yields (90-96%). The reactions of calchone oxide (10) with thiols 2b-d have exclusively resulted in the formation of beta-carbonylsulfides 10b-d (82-93% yield), coming from the nucleophilic attack at the alpha-position and retroaldol condensation. To highlight the synthetic utility of this procedure, one-pot multisteps preparation of vinyl sulfides 7b and 7c, vinyl sulfoxides 12 and 13, and 1,5,6,7-tetrahydro-4H-1,2,3-benzotriazol-4-one (14) starting from 2-cyclohexen-1-one (11) have also been reported.

3-nitrocoumarins as dienophiles in the Diels-Alder reaction in water. An approach to the synthesis of nitrotetrahydrobenzo[c]chromenones and dihydrodibenzo[b,d]furans.

The [4 + 2] cycloadditions of 3-nitrocoumarin (1a), 6-chloro-3-nitrocoumarin (1b), and 6-, 7-, and 8-hydroxy-3-nitrocoumarins (1c, 5, and 6) with (E)-piperylene (7), isoprene (8), 2,3-dimethyl-1,3-butadiene (9), 2-methoxy-1,3-butadiene (10), 2,3-dimethoxy-1,3-butadiene (11), and cyclopentadiene (12) were investigated in aqueous medium, in organic solvent and under solventless conditions. The reactions performed in water occurred in heterogeneous phase but were faster than those executed in toluene or dichloroethane (DCE). 1a-c, 5, and 6 behaved as 2pi components in the Diels-Alder cycloadditions with 7-10 and 12, and exo adducts were preferentially or exclusively produced. Surprisingly 1a, behaved as a 4pi component in the cycloaddition in water with 11 and 4-substituted 3-nitrochromanones 20 and 21 were isolated. The cycloadditions of hydroxy-3-nitrocoumarins 1c, 5, and 6 with 1,3-diene 9 did not work in water or in organic solvent, but did work under solventless conditions. Nitrotetrahydrobenzo[c]chromenones 13-16, 24, and 25, originating from the normal electron-demand Diels-Alder reactions, were converted into dihydrodibenzo[b,d]furans 27-31 in water, via one-pot Nef-cyclodehydration reactions.

Zn(II)-catalyzed thiolysis of oxiranes in water under neutral conditions.

Thiolysis of a variety of 1,2-epoxides in water at 30 degrees C and pH 7.0 is strongly accelerated by ZnCl(2) (10 mol %) except when amino- and carboxythiophenol are used. The aqueous medium and the catalyst were recovered and reused in various runs without affecting the efficiency of the process.

First one-pot copper-catalyzed synthesis of alpha-hydroxy-beta-amino acids in water. A new protocol for preparation of optically active norstatines.

Alpha-hydroxy-beta-amino acids were synthesized with excellent yields for the first time in water and by a simple procedure based on a copper catalytic cycle, which included the recovery and reuse of the catalyst and is possible to realize by using only water as reaction medium.