Bromolactonization, enantioselective

Scheme 36.34 Enantioselective organocatalytic bromolactonization of c/s-enynes (NBS = N-bromosuccinimide).

An efficient and enantioselective bromolactonization of 1,2-disubstituted ole-finic acids has been developed by Yeung et al. [99] (Scheme 54). Reaction of olefinic acid 262 with NBS in the presence of 10 mol% of quinidine-derived aminothiocarbamate catalyst 263 afforded 8-lactone 264 in excellent yield and with excellent enantioselectivity. 

A similar catalytic enantioselective bromolactonization of enyne carboxylic acids has been reported by Tang et al. [100] (Scheme 55). Treatment of 265 with NBS in the presence of 20 mol % of catalyst 267 obtained by tethering a cinchona alkaloid skeleton to an urea group afforded bromoallenyl-8-lactone 266 in excellent yield and with good enantioselectivity. 

An enantioselective bromolactonization has been reported for the benzoic acids with an ortto-vinylic substituent (7) the reaction proceeds readily on treatment with NBS in the presence of the amino-thiocarbamate organocatalyst. ... 

The binaphthyl-type bifunctional catalyst (11) has been developed to promote the enantioselective bromolactonizations of unsaturated acids (9). Notably, unlike with other catalysts, this reaction is not only efficient with of 4- and 5-aryl-4-pentenoic acids, but also with 5-alkyl-4(Z)-pentenoic acids. Furthermore, it represents the first catalytic bro-... 

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