PALLADIUM CATALYZED THIENYLATION OF ALLYLIC ALCOHOLS WITH 2-BROMOTHIOPHENE AND 3-BROMOTHIOPHENE AND THEIR DERIVATIVES

Pd catalyzed reaction of allylic alcohols with 2-bromothiophene provides 3-(2'-thienyl)aldehydes or ketones selectively together with the small amounts of 2-(2'-thienyl)aldehydes and ketones. Similarly 3-(3'-thienyl)-aldehydes or ketones were obtained selectively from allylic alcohols and 3-bromothiophene. The reactivity and regioselectivity largely depend on the solvents, additives, and the structure of allylic alcohols. Generally aprotic dipolar solvent such as HMPA and DMF gave the most satisfactory results. 2-Thienyl iodide showed somewhat higher reactivity than 2-thienyl bromide. 2-Thienyl chloride was unreactive. Sodium iodide and/or triphenyl-phosphine were very effective as the cocatalysts especially for the reactions to give aldehydes. This thienylation reaction was also applicable to 2-bromothiophenes with a wide variety of substituents at 5-position. The synthetic utility of this catalytic reaction has been illustrated by the synthesis of 9-oxo-trans-2-decenoic acid (Queen substance). © 1979.