Trimethylsilyl enol ethers are successively converted into chirally protected α-formyl ketones by asymmetric formylation with the 2-methoxy-1,3-oxazolidine 2, transformed into the corresponding, thermodynamically determined (Z)-TMS enol ethers, and then are allowed to condense with aldehydes. All steps proceed with high stereoselectivity. Some synthetic options, arising from the three differentiated oxygen functionalities in the intermediates 8 are illustrated for the title target compounds.
三甲基
硅基烯醇醚通过与2-甲氧基-1,3-
噁唑啉-2的非对称
甲醛化反应,依次转化为具有手性保护的α-甲酰基酮,随后转化为相应的热力学确定的(Z)-TMS烯醇醚,再与
醛类发生缩合。所有步骤均具有较高的立体选择性。文中对中间体8中的三种不同氧官能团所带来的合成选择进行了阐述,以便为目标化合物提供合成途径。