Atroposelective ring

The mechanism of the atroposelective ring opening of a lactone-bridged biaryl, dinaphtho[2,l-t l, 2 -< ]oxepin-3(5//)-one, with a chiral oxazaborolidine-BH3 complex (Scheme 2) was studied using semi-empirical AMI calculations <2000JOC2517>. 

An efficient atropo-enantioselective total synthesis of the axially chiral bicoumarin (+)-isokotanin was accomplished by J. Bringmann and co-workers.The key steps in this synthetic approach were the formation of a configurationally stable seven-membered biaryl lactone by the Cannizzaro reaction of the corresponding biaryl dialdehyde followed by a kinetic resolution by atroposelective ring cleavage. 

Both total syntheses of Evans et al. and Nicolaou et al. first perform synthesis of the AB/C-O-D-ring systems before condensation with the D-O-E ring system. The Evans et al. route was extended by several synthetic steps by the conversion of the 2-OH-group of Hpg and the conversion of nitro substituents after SnAt into hydrogen substituents. Problems developed with the transformation of the C-terminal amide into the carboxy function during deprotection steps. In contrast, Nicolaou et al. had to face the relatively moderate atroposelectivities and had to solve the somewhat obscure conversion of the triazene into a phenolic group. Both syntheses have been compared and discussed in the literature. ... 

Dynamic kinetic resolution atroposelective lactone ring opening and its use in the synthesis of natural products and chiral auxiliaries 03T8291. 

As part of their investigations towards the synthesis of the cytotoxic marine natural product diazonamide A, Feldman et al. discovered a noteworthy atroposelective macrolactonisation reaction. Thus, the ring closure of the configurationally flexible model bisindole depicted in Scheme 5.29 afforded the corresponding lactone as a single isomer. The bulk of the NB0C2 group was... 

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