Aldehyde addition and copper-mediated allylation of bicyclic alkoxytitanacyclopentenes and -pentadienes: New selectivities and an unusual reaction

Bicyclic titanacyclopentenes generated in situ from 1,6-enynes and (eta(2)- propene)Ti(O-i-Pr)(2) (1) reacted with aldehydes at their alkenyl-titanium bond in the absence or presence of Ti(O-i-Pr)(n)Cl4-n (n = 2 or 3) to give allyl alcohols such as 5-7 as a nearly single stereoisomer in good yields. Upon workup with DCl/D2O or iodine, deuterio and iodo derivatives, 8 and 9, were obtained. Bicyclic titanacyclopentadienes prepared analogously from 1 ,6- or 1,7-diynes and 1 also reacted with aldehydes in the presence of an a dditional equivalent of Ti(O-i-Pr)(2)Cl-2 to afford 1,2-dialkylidenecyclope ntanes pr -cyclohexanes having an alcohol moiety in their side chain in goo d yields. In place of the simple hydrolysis, deuteriolysis or iodinolysis g ave the corresponding derivatives such as 21 or 22. Treatment of 1,6-enyne 10 with 1 in the standard way and then with a slight excess of i-PrMgCl at -50 degrees C generated a new titanium species that, upon reaction with ald ehydes, afforded unexpected adducts 34 and 41-45 virtually as a single isom er. Copper-mediated allylation of dialkoxytitanacyclopentene such as 3 with allyl bromide proceeded at their vinyl-titanium bond to give 48 and 50. Li kewise, dialkoxytitanacyclopentadiene prepared from 29 and 1 underwent the regioselective copper-mediated mono-allylation to give a 9:1 mixture of 53 and 54. Upon workup with deuteriochloric acid, the corresponding deuterated product was obtained with a high degree of deuterium incorporation.