Alkylation of lithiated dimethyl tartrate acetonide with unactivated alkyl halides and application to an asymmetric synthesis of the 2,8-dioxabicyclo[3.2.1]octane core of squalestatins/zaragozic acids
作者:Herman O Sintim、Hamad H Al Mamari、Hasanain A A Almohseni、Younes Fegheh-Hassanpour、David M Hodgson
DOI:10.3762/bjoc.15.116
日期:——
5-tricarboxylate-2,8-dioxabicyclo[3.2.1]octane core 31 of squalestatins/zaragozic acids. Furthermore, monoalkylated tartrates 33a,d,f, and 38a on reaction with NaOMe in MeOH at reflux favour (≈75:25) the cis-diester epimers epi-33a,d,f and epi-38a (54–67% isolated yields), possessing the R,S-configuration found in several monoalkylated tartaric acid motif-containing natural products.
(R,R)-酒石酸二甲酯丙酮酸7在THF / HMPA中经历LDA脱质子反应,并在-78°C下与一系列烷基卤化物(包括未活化的底物)在-78°C下反应,得到单一的非对映异构体(在单烷基化酒石酸盐的丙酮化合物)17,24,33A-F ,38A,38B,41的R,R构型,即,stereoretentive过程(13-78%产率)。在这些条件下,可以少量(9–14%)联产可分离的反式二烷基酒石酸酯34a–f,这很可能是由酒石酸酯的非手性二烯酸36引起的。7。从γ-甲硅烷基氧烷基碘化物衍生的烷基化酒石酸酯17和24中的乙醇酸酯氧化和乙炔化物去除,分别得到酮21和26,然后是Bamford-Stevens衍生的重氮酸酯23和27。只有三乙基甲硅烷基保护的重氮酯27被证明可以递送重氮酮28。后者经历了立体选择性羰基内酯的形成-与乙醛酸甲酯的环加成反应以及所得环加合物29的酸催化重排,得到3,4,5-三羧酸酯-2