Anderson James C, Ford J Gair, Whiting Matthew
School of Chemistry, University of Nottingham, Nottingham, UKNG7 2RD.
Org Biomol Chem. 2005 Oct 21;3(20):3734-48. doi: 10.1039/b510756c. Epub 2005 Sep 12.
The aza-[2,3]-Wittig sigmatropic rearrangements of substrates derived from enantiomerically pure alanine, valine and serine with phenyl and ester anion stabilising groups were investigated for their efficiency in chirality transfer. It was found that a methyl substituent at the stereogenic centre of the rearrangement precursors was inadequate to control the alkene stereoselectivity and enantioselectivity of the rearrangement. Ester stabilised anions of valine and serine derivatives were the most successful with up to 66% yield, 14 : 1 alkene (E)-stereoselection and 88% chirality transfer. A limitation to the steric bulk of the stereogenic centre was noted in that the substituent has to be bulky enough to dictate alkene stereoselection, but not too large to compromise the directing effect of the activating phenyldimethyl silyl substituent on the anion stabilising group. Experimental evidence suggested a possible complimentary coordinating effect of an O-MOM serine substituent, which may assist alkene stereoselectivity and enantioselectivity.
研究了由对映体纯的丙氨酸、缬氨酸和丝氨酸衍生的带有苯基和酯阴离子稳定基团的底物的氮杂-[2,3]-维蒂希（aza-[2,3]-Wittig）σ-迁移重排反应在手性转移方面的效率。结果发现，重排前体的手性中心处的甲基取代基不足以控制重排反应的烯烃立体选择性和对映选择性。缬氨酸和丝氨酸衍生物的酯稳定阴离子最为成功，产率高达66%，烯烃（E）-立体选择性为14:1，手性转移率为88%。注意到手性中心空间位阻的一个限制，即取代基必须足够大以决定烯烃的立体选择性，但又不能太大而损害活化苯基二甲基硅烷基取代基对阴离子稳定基团的导向作用。实验证据表明O-甲氧基甲基（O-MOM）丝氨酸取代基可能存在互补配位作用，这可能有助于烯烃的立体选择性和对映选择性。
