title: Chirality transfer in the aza-[2,3]-Wittig sigmatropic rearrangement.
abstract: 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.
authors.affiliation: School of Chemistry, University of Nottingham, Nottingham, UKNG7 2RD. j.anderson@nottingham.ac.uk
authors.forename: James C
authors.initials: JC
authors.lastname: Anderson
authors.forename: J Gair
authors.initials: JG
authors.lastname: Ford
authors.forename: Matthew
authors.initials: M
authors.lastname: Whiting
mesh_terms: D000596:Amino Acids / Q000737:chemistry*; D001372:Aza Compounds / Q000737:chemistry*; D015394:Molecular Structure; D012821:Silanes / Q000138:chemical synthesis* / Q000737:chemistry; D013237:Stereoisomerism
chemical_list: D000596:Amino Acids; D001372:Aza Compounds; D012821:Silanes