Synthetic Applications of Stereodefined 2-Substituted 1-Silyl-1-stannylethenes: A New Synthesis of 5-Ethenyl-5′-(1-propynyl)-2,2′-bithiophene, a Naturally-Occurring Phototoxin)

Abstract

(E)-2-(5-Trimenthylstannyl-2-thienyl)ethenyldimethylphenylsilane. (E)-8, which can be stereospecifically prepared from (Z)-1-dimethylphenylsilyl-2-(2-thienyl)-1-trimethylstannyl-ethene, (Z)-6, or from (E)-2-(2-thienyl)ethenyldimethylphenylsilane, (E)-9, serves as an equivalent to the 2-ethenylthiophene d ¹', d ⁵-synthon, 20, in an efficient two-step synthesis of 5-ethenyl-5′-(1-propynyl)-2,2′-bithiophene, 10, a naturally-occurring phototoxin. In the first step of this synthesis compound (E)-8 undergoes a palladium-catalyzed cross-coupling reaction with 2-iodo-5-(1-propynyl)thiophene, 16, and in th second step the so obtained cross-coupling product, (E)-17, undergoes a protodesilylation reaction.