Titanium alkoxide-based method for stereoselective synthesis of functionalized conjugated dienes

Treatment of an internal acetylene such as 1-silyl-1-octyne (3) with a low- valent titanium reagent, (eta(2)-propene)Ti(O-i-Pr)(2) (1) readily prepared from Ti(O-i-Pr)(4) and i-PrMgCl in situ, generates an acetylene-titanium c omplex. This complex was allowed to react with a terminal acetylene, 4-(ben zyloxy)-1-butyne (5), to give the intermediate titanacyclopentadiene (6) wh ich, upon hydrolysis, deuteriolysis, or iodinolysis, gave diene 8, or its b is-deuterated (>99% d(2)) and bis-iodinated counterparts (9 and 10), in goo d yields and with high selectivities. This reaction is applicable to the cr oss-coupling reaction of functionalized acetylenes such;as 2-allynoates and 2-alkynamides 12-18 and a variety of terminal acetylenes 24-28 to give die nes 36-50 in good yields. A terminal acetylene 28 carrying an olefinic bond at the other terminus reacted with a silylpropiolate to afford the expecte d diene 42 without any complication.