Butenolide, enantioselectic allylic

The enantioselective total synthesis of (-l-)-aflatoxin Bi has been achieved by O-allylation with y-acyloxybutenolide and reductive Heck reaction [76]. The couma-rin derivative 199 was 0-allylated with y-O-Boc-butenolide 200, which is an... 

In the course of developing an easy access to chiral y-butenolides, Shi et al. have established an efficient multifunctional chiral binaphthyl phosphine-catalysed allylic substitution of Morita-Baylis-Hillman acetate with 2-tri-methylsiloxy furan. The regjospecific allylic substitution occurred to provide the xyra-y-butenolide in good to excellent yield, high regjoselectivity and excellent enantioselectivity by using water as an additive. The scope of this reaction could be successfully extended to a variety of Morita Baylis Hillman acetates, as shown in Scheme 5.10. 

Mao B, Geurts K, Fananas-Mastral M, van Zijl AW, Fletcher SP, Minaard AJ, Feringa BL (2011) Catalytic enantioselective synthesis of naturally occurring butenolides via hetero-allylic alkylation and ring closing metathesis. Org Lett 13 948-951... 

B. Mao, Y. Ji, M. Fananas-Mastral, G. CaroH, A. Meetsma, B.L. Feringa, Highly enantioselective synthesis of 3-Substituted y-butenolides by palladivun-catalyzed kinetic resolution of unsymmetrical allyl acetates, Angew. Chem. Int. Ed. 51 (2012) 3168-3173. 

Scheme 5.44 Enantioselective formation of butenolides 133 by palladium-catalyzed decarboxylative allylic alkylation of furan-derived enol carbonate 132.

Calcium alginate-immobilized yeast cells were successfully used for the synthesis of small peptides [524]. Of special synthetic mterest seems to be the biohydrogenation of 2-substituted allyl alcohols 355 (Fig. 86) to afford enantioselectively the (/ )-2-methylal-kanols 356 [525,526]. For natural product synthesis several butenolides have been reduced very successfully with BY [527-529]. 

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