Acid allyl esters regiospecific

Stereoselective synthesis of (+)-K252a (5) has been reported from a pentose derivative (Schemes 3 and 4). Esterification of the indole 3-acetic acid (27) with allyl bromide afforded the corresponding ester, which nnderwent regiospecific bromination with NBS to give the corresponding 2-bromoindole 28 whose glycosylation with l-chloro-2-deoxy-... 

Posner and colleagues have recently made use of a [3,3]-sigmatropic rearrangement of an a,P-unsaturated sulfoxide as part of a regiospecific conversion of allylic alcohols into two-carbon-extended conjugated dienoate esters [233]. For example, reaction of allyl alcohol (291) with the sulfinyl orthoester (292) and a catalytic amount of 2,46-trimethylbenzoic acid in dichloromethane at 100°C produced ethyl pentadienoate (295) in 75% yield. The reaction is believed to... 

Propargylic alcohols react with carboxylic acids, DEAD, and TPP to give the corresponding inverted esters without formation of allenic alcohols. Similarly, in allylic alcohols where no bias exists against the normal Sn2 process, clean regiospecific inversion is invariably observed or implied. - In specific cases where the Sn2 pathway is hindered for some reason, such as eclipsing of substituents, aUylic rearrangement can occur (eqs 11-13). When compound (11) reacts with benzoic acid, DEAD, and TPP, (13) and (14a,b) (a/b=4 l) are obtained in a ratio of 1 1. Similar treatment of (11) in the presence of PdCla (0.1 equiv) results in... 

---