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

(E)-2-(5-Trimethylstannyl-2-thienyl)ethenyldimethylphenylsilane, (E)-8, which can be stereospecifically prepared from (Z)-1-dimethylphenylsilyl-2-(2-thienyl)-1-trimethylstannylethene, (Z)-6, or from (E)-2-(2-thienyl)ethenyldimethylphenylsilane, (E)-9, serves as an equivalent to the 2-ethenylthiophene d1', d5-synthon, 20, in an efficient two-step synthesis of 5-ethenyl-5'-(1-propynyl)-2,2'-bithiophene, 10, a naturally-occurring photoxin. 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 the second step the so obtained cross-coupling product, (E)-17, undergoes a protodesilylation reaction.