Stereoselective synthesis of 3,4-disubstituted pyroglutamates by ring transformation of 5-ylidene-1,3-dioxan-4-ones with N-(diphenylmethylene)-glycinate
摘要:
N-(Diphenylmethylene)-glycinate gives stereoselective conjugate addition to readily available (E) and (Z)-5-ylidene-1,3-dioxan-4-ones. Hydrolytic cleavage of the imine functionality of the resulting Michael-adducts causes ring transformation to new, optically active 3,4-disubstituted pyroglutamates. (C) 2000 Elsevier Science Ltd. All rights reserved.
Stereoselective Synthesis of Thiochroman-4-ones by Ring Transformation of Chiral 5-Ylidene-1,3-dioxan-4-ones with 2-Bromothiophenol via Bromo−Lithium Exchange
The reaction of (E)- or (Z)-5-ylidene-1,3-dioxan-4-one (1) and 2-bromothiophenol, followed by bromo-lithium exchange with nBuLi, provides a new access to optically active thiochroman-4-ones 4 and 5. Stereoselective conjugate addition occurs in the first step and the resulting 5-(1-phenylsulfanylalkyl)-1,3-dioxan-4-ones 2 and 3 undergo ring transformation to thiochroman-4-ones by attack of the lithiated phenyl ring at the dioxanone carbonyl carbon atom, cleaving off pivalaldehyde. If reactants with a (Z)-configuration are used, a retro-aldol reaction occurs in the ring transformation step, thus affording the 3-unsubstituted thiochroman-4-ones 5 rather than 3-(l-hydroxyethyl)-thiochroman-4-ones 4. This phenomenon can be rationalized by the steric congestion in the intermediate enolate 7.
Stereoselective Diazoalkane Cycloadditions to Chiral 5-Alkylidene-1,3-dioxan-4-ones and 3-Benzylidene-β-lactones
作者:Annett Bartels、Peter G. Jones、Jürgen Liebscher
DOI:10.1055/s-1998-2195
日期:1998.11
AMBERG, WILLI;SEEBACH, DIETER, CHEM. BER., 123,(1990) N2, C. 2413-2428
作者:AMBERG, WILLI、SEEBACH, DIETER
DOI:——
日期:——
AMBERG, WILLI;SEEBACH, DIETER, CHEM. BER., 123,(1990) N2, C. 2429-2438