Substituted chromans and tetrahydrofuro[2,3‐b]benzofurans (trapped tetrahedral intermediates) from 3‐phenyl‐2‐benzofuranones

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Abstract
The previously discovered neighboring group reaction has been extended to the synthesis of chroman derivatives (i.e., 4, 5, 6) containing geminal methyls in the 2‐position, a feature common to certain physiologically active natural chromans. In two instances, cyclic ortho ester by‐products (8), not observed in previous work, were formed as a result of the intramolecular trapping of tetrahedral intermediates. Reasons for the incursion of this unexpected side reaction are discussed.