Aldehyde Addition and Copper-Mediated Allylation of Bicyclic Alkoxytitanacyclopentenes and -Pentadienes: New Selectivities and an Unusual Reaction

Abstract

Bicyclic titanacyclopentenes generated in situ from 1,6-enynes and (η2-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)nCl4-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 additional equivalent of Ti(O-i-Pr)2Cl2 to afford 1,2-dialkylidenecyclopentanes or -cyclohexanes having an alcohol moiety in their side chain in good yields. In place of the simple hydrolysis, deuteriolysis or iodinolysis gave 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 °C generated a new titanium species that, upon reaction with aldehydes, afforded unexpected adducts 34 and 41−45 virtually as a single isomer. Copper-mediated allylation of dialkoxytitanacyclopentene such as 3 with allyl bromide proceeded at their vinyl−titanium bond to give 48 and 50. Likewise, 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.