Construction of Quaternary Stereogenic Centers via [2 + 2] Cycloaddition Reactions. Synthesis of Homochiral 4,4-Disubstituted 2-Azetidinones and Imine Substituent Effects on β-Lactam Formation
作者:Claudio Palomo、Jesus M. Aizpurua、Jesus M. García、Regina Galarza、Marta Legido、Raquel Urchegui、Pascual Román、Antonio Luque、Juan Server-Carrió、Anthony Linden
DOI:10.1021/jo962017z
日期:1997.4.1
A study on the asymmetric construction of quaternary stereogenic centers via [2 + 2] cycloadditionreaction of ketenes with ketimines is described. Reaction of achiral ketenes and chiral alpha-alkoxy ketone-derived imines resulted in formation of new beta-lactams as single diastereomers. The cycloaddition was extended to pyruvate imines, aralkyl ketone-derived imines, and dialkyl ketimines. In these
TiCl4-mediated aldol reactions of chiral methyl α-silyloxy ketones with a variety of aldehydes provide the corresponding 1,4-syn aldol adducts with moderate to high stereocontrol. This transformation represents a new approach to substrate-controlled acetate aldol reactions and complements the 1,4-anti asymmetric induction produced by the related α-benzyloxy ketones. This new approach could be useful
α-tert-butyldimethylsilyloxy ketones followed by reduction of the resultant aldolates with LiBH4 provides a straightforward access to syn-1,3-diols. These diols, containing up to three new stereocentres, can be easily isolated in high yields after a simple work-up without any additional oxidative treatment, which confers to this procedure an appealing position to prepare stereoselectively such sort of structures
Good levels of 1,4-syn asymmetric induction are obtained in the TiCl4-mediated aldol reaction of methyl α-silyloxy ketones with achiral aldehydes. Such methodology represents a new approach to the substrate-controlled acetate aldol reaction, which can be useful to design more efficient syntheses of natural products.