Nareshkumar F. Jain

Asymmetric Synthesis of Homoallylic Amines and Functionalized Pyrrolidines via Direct Amino-Crotylation of In Situ Generated Imines

Abstract The asymmetric synthesis of functionalized homoallylic amines and silyl functionalized pyrrolidines through the Lewis acid promoted condensation of chiral (E)-crotylsilanes with sulfonyl imines and in situ generated N-acyl imines is described. We had anticipated that this bond construction could be used in the asymmetric synthesis of the N-terminal amino acid subunit of the nikkomycins. Aryl sulfonyl imines condense with chiral silane reagents in the presence of BF3·OEt2 to form homoallylic arylsulfonyl amines with useful levels of syn selectivity. For cases involving aryl N-acyl imines we have learned that the temperature controls the course of the reaction. For instance, at temperatures of −78°C or below the major product is the pyrrolidine, while at higher temperatures (−30 to −20°C) the homoallylic amine is produced. For the cases studied, the [3+2]-annulation is limited to aryl imine derivatives, as alkyl- and branched- imines failed to produce the pyrrolidine derivatives: higher reaction temperatures promote the conversion of the annulation product to the homoallylic amines. In double stereodifferentiating reactions with in situ generated imines, good levels of selectivity were achieved in the formation of secondary amines bearing syn–anti and syn–syn stereochemical triads.

Diastereoselectivity in cyclopropanation and epoxidation reactions of chiral (E)-crotylsilanes: Asymmetric synthesis of substituted tetrahydrofurans

Functionalized (E)-crotylsilanes 1 bearing a bis-homoallylic hydroxyl group undergo diastereoselective cyclopropanation and epoxidation reactions to produce substituted tetrahydrofurans 3 and 5 respectively after an acid catalyzed heterocyclization.

An efficient procedure for the preparation of chiral β-substituted (E)-crotylsilanes: Application of a rhodium(II) catalyzed silylformylation of terminal alkynes

Abstract Functionalized β-substituted ( E )-crotylsilanes ( R )-7 and ( S )-8, bearing an alkyl or aryl group adjacent to the stereogenic C-Si center have been synthesized in an efficient four-step procedure initiated with a regio- and stereoselective silylformylation of a terminal alkyne catalyzed by dirhodium(II) perfluorobutyrate.

Double stereodifferentiation in the lewis acid promoted crotylation of (S)-2-Alkoxypropanal with chiral β-Alkyl (E)-Crotylsilanes

Abstract The sense and level of 1,2-asymmetric induction have been evaluated in the Lewis acid promoted addition of ( E )crotylsilanes ( S )-1 and ( R )-2 to ( S )-2-alkoxypropanal 3 and 7. These aldehydes are substituted at the α-position with benzyloxy (OBn) to reinforce chelation and tert-butyldiphenylsilyloxy (TBDPSO) groups to prevent chelation with bidentate Lewis acids. The nature of the Lewis acid and the chirality of the silane reagent were found to playa pivotal role in the direction and levels of carbonyl diastcreoface selectivity.

Application of chiral (E)-crotylsilanes in synthesis: The asymmetric synthesis of the C1C17 polypropionate fragment of rutamycin B

The asymmetric synthesis of the polypropionate fragment of rutamycin B is reported employing chiral allylsilane bond construction methodology for the introduction of six of the nine stereogenic centers. In this paper, the construction of the C3C12 subunit and its coupling to the aldehyde 12 through a Mukaiyama-type aldol reaction are described.

Application of chiral (E)-crotylsilanes in synthesis: The asymmetric synthesis of the C19C34 spiroketal fragment of rutamycin B

Abstract The asymmetric synthesis of the spiroketal fragment of rutamycin B is reported employing allylsilane bond construction methodology for the introduction of five of the eight stereogenic centers. In this paper, the construction of the C19C28 and C29C34 fragments as well as their coupling through an alkylation reaction of a lithiated N , N -dimethylhydrazone are described.