Base-Induced Cyclisations of o-Ethynylaryl-Substituted Benzyl Alcohols

In a study of the base-induced cyclisations of o-ethynylaryl-substituted benzyl alcohols it was found that substrates la-c reacted smoothly and exclusively by 5 -exo-dig ring closure to give the isobenzofuran derivatives 2a-c. Thus, treatment of la with KOH/MeOH gave 2a in 95% yield 2b and 2c were obtained in quantitative yield by treatment of lb and lc with NaH in THF. 

Under the same conditions of NaH/THF, the ester 3 gave ltf-2-benzopyran derivative 5 in 60% yield, apparently by 6-endo-dig ring closure. Closer study of this latter transformation, however, revealed that the initial product of base-induced cyclisation was in fact the isobenzofuran 4, which was extremely labile, and that 5 was formed from 4 by acid-catalysed rearrangement during work-up of the reaction mixture. 

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