ABSTRACT
A simple and efficient synthetic route to various 1,4-disubstituted tetrahydro-ß-carbolines and tetrahydropyrano[3,4-b]indoles in high yields and stereoselectivity via LiClO4-catalyzed SN2-type ring opening of aziridines and epoxides with indoles followed by p-toluenesulfonic acid (PTSA) catalyzed Pictet-Spengler reaction is described.
ABSTRACT
Direct and expedient access to densely substituted tetrahydrocarbazoles and tetrahydrocycloheptadiindoles bearing multiple contiguous stereocentres has been achieved via a two-fold divergent diastereoselective (dr up to >99 : 1) transformation of 2-vinylindoles. The high-yielding conversions (yield up to 87%) that are amenable for a wide range of substituted 2-vinylindoles proceed through Lewis acid-catalyzed [4 + 2] and [4 + 3] cyclization-aromatization cascade reactions, respectively, involving a heretofore-unprecedented reversal of the polarity (umpolung) of 2-vinylindoles. The two synthetic routes are effortlessly transposable into each other by merely modulating the temperature to furnish the corresponding products in a selective and exclusive fashion. In addition, another novel synthetic route to tetrahydroindolocarbazoles has been developed that advances via a formal [4 + 2] cyclization of 4-vinylindoles involving sequential C3 Michael addition-dearomatization-aromatization cascade reactions.
ABSTRACT
An efficient and green "on water" regio- and stereoselective synthetic route to chiral 1,2,4-oxadiazinanes and 1,4,2-dioxazinanes with excellent yields (up to 99%) and de/ee (>99%) has been developed for the first time via the domino ring-opening cyclization (DROC) of N-activated aziridines and epoxides with nitrones using LiClO4/Bu4NBF4 a dual catalyst system. The developed green strategy features a broader substrate scope and mild reaction conditions, and successfully overcomes the competitive oxidative ring opening of aziridines. Further synthetic significances of this green protocol are the formation of the products (i) as single diastereomers starting from a mixture of cis/trans disubstituted aziridines via dynamic kinetic epimerization (DKE) and (ii) via a multicomponent approach starting from N-methyl hydroxylamine hydrochloride, benzaldehyde and aziridine.
ABSTRACT
A simple and efficient strategy for the synthesis of various 1,4-disubstituted tetrahydro-ß-carbolines with excellent stereoselectivity (de, ee up to >99%) via domino ring opening cyclization (DROC) of activated aziridines with 2-vinylindoles is described. The reaction proceeds through LiClO4-catalyzed Friedel-Crafts-type alkylation of 2-vinylindoles with activated aziridines followed by an intramolecular aza-Michael reaction in a domino fashion.
ABSTRACT
A highly enantioselective synthetic route to hexahydropyrrolo[2,3-b]indoles via Lewis acid-catalyzed SN2-type ring opening of activated aziridines with indoles having substitutions at 3- and other positions followed by cyclization in a domino fashion has been developed. Hexahydropyrrolo[2,3-b]indoles have been detosylated in the same pot to afford the corresponding products with free NH group in excellent yields (up to 95%) and enantioselectivity (up to >99%).
ABSTRACT
A new synthetic route to nonracemic tetrahydropyrrolo[2,3-b]indoles has been developed via SN2-type ring opening of enantiopure N-activated aziridines with 2-bromoindoles followed by copper-catalyzed C-N cyclization. A series of N-activated aziridines and 2-bromoindole derivatives with different substitution patterns were studied to afford the corresponding tetrahydropyrrolo[2,3-b]indoles in good yields and excellent ee (up to 99%). Highly substituted tetrahydropyrrolo[2,3-b]indole was synthesized as a single stereoisomer (de, ee >99%) from enantiopure trans-disubstituted aziridine.
ABSTRACT
A simple strategy for the syntheses of 2-alkyl indoles via regioselective ring-opening of 2-(2-haloaryl)-3-alkyl-N-tosylaziridines with thiophenol, followed by copper powder-mediated intramolecular C-N cyclization and subsequent aromatization by the elimination of thiophenol, with good yields is described. Utilizing this protocol, 2-carboxyindole has been synthesized easily.
ABSTRACT
A simple protocol for the synthesis of dihydrobenzothiazines through regio- and stereoselective S(N)2-type ring opening of N-tosylaziridines with sulfur nucleophiles followed by copper-powder-mediated intramolecular C-N cyclization in excellent yields (up to 95%) with high diastereo- and enantioselectivity (up to >99%) is reported.
Subject(s)
Aziridines/chemistry , Benzene Derivatives/chemical synthesis , Copper/chemistry , Phenols/chemistry , Sulfhydryl Compounds/chemistry , Thiazines/chemical synthesis , Aziridines/chemical synthesis , Benzene Derivatives/chemistry , Cyclization , Phenols/chemical synthesis , Stereoisomerism , Sulfhydryl Compounds/chemical synthesis , Thiazines/chemistryABSTRACT
A simple strategy for the synthesis of chiral α,ß-diamino- and α-amino,ß-hydroxy ester derivatives in high yields with moderate to high ee has been developed via asymmetric imino-aldol and aldol reactions, respectively, starting from protected aminoesters employing memory of chirality concept for chiral induction. This strategy has been extended for the enantioselective synthesis of aziridines (ee up to 92%). The absolute configuration of the imino-aldol adducts has been determined. The stereochemical outcome of the products has been explained by a suitable mechanism and supported by computational studies.
