129372-66-3Relevant academic research and scientific papers
Stereospecific reaction of an α-sulfonyl carbanion through chelation
Singh, N. P.,Metz, B.,Biellmann, J. F.
, p. 98 - 107 (2007/10/02)
Intramolecular chelation as presented in formula 6 is proposed to explain asymmetric induction of reactions of the carbanion derived from sulfone 10.The designed molecule 10 was obtained from reaction of camphor lithium enolate derived from (+)-camphor (1R,4R bornan-2-one) with sulfur dioxide followed by 3-methyl-2-butenyl bromide to give the keto sulfone 9 which was reduced by LAH to the hydroxysulfone 10.The dianion prepared by action of n-butyllithium gave, with methyl iodide, the mono-methylated product 14 with a diastereomeric excess better than 96percent.The structure of the methylated product was determined by X-ray diffraction.The R configuration at the new asymmetric carbon corresponds to an inversion in the methylation reaction if the species has a chelated structure like 6.With excess of methyl iodide, the C- and O-methylated product 15 was obtained.In the presence of HMPA, the stereoselectivity was lower.The reaction of the carbanion derived from sulfone 10, with methyl 3-methylbut-2-enoate requires the presence of HMPA and leads to chrysanthemic ester 17 with 25percent e.e.
