Regioselectivity in the Addition of Grignard Reagents to Bis(2‐benzothiazolyl) Ketone: C ‐ vs. O ‐Alkylation Using Aryl Grignard Reagents

The reaction between bis(2‐benzothiazolyl) ketone ( 1 ) and a series of ring‐substituted phenyl Grignard reagents gives, in considerable amount, the unexpected O ‐alkylation product derived from the attack of the Grignard reagent to thecarbonyl oxygen atom, thus extending the range of rarely reported cases in which O ‐alkylation can occur. The expected classic 1,2‐addition product and that derived from O ‐alkylation have been obtained in a relative molar ratio dependent on the substituent on the phenyl ring. Bis(2‐benzothiazolyl) aryl carbinols, the classic 1,2‐addition products to the carbonyl group of 1 , were obtained in high yield through an alternative synthetic route that permitted the limit imposed by O ‐ vs. C ‐alkylation competition to be overcome.