Reagent controlled addition of chiral sulfur ylides to chiral aldehydes

• Varinder K. Aggarwal and
• Jie Bi

Beilstein J. Org. Chem. 2005, 1, No. 4, doi:10.1186/1860-5397-1-4

• earlier studies we had established that the degree of reversibility in betaine formation could be influenced by the degree of solvation of the intermediate alkoxide. The initially formed betaine 9 with charges gauche to each other can either undergo bond rotation to betaine 10 followed by ring closure to

• give the epoxide 7a or reversion to the ylide and the aldehyde. Solvation of the alkoxide 9 reduces the barrier to bond rotation rendering reactions less reversible. We therefore examined the same reactions in the presence of LiCl (Table 1, entries 4, 6). Now increased C1 selectivity (C1(R):C1(S), 96:4

• that influenced reversibility in betaine formation included ylide stability, solvation of the metal alkoxide and steric hindrance around the aldehyde and ylide.[2] We now add another factor to this growing list: stereochemistry of the aldehyde. Evidently, in one isomer, the groups between the aldehyde