Convergent synthesis of fully functionalized ring C allocolchicinoids. Benzannulation approach

[GRAPHICS] A novel convergent approach to fully functionalized ring C allocolchicinoid s is developed which is based on the benzannulation reaction of Fischer car bene complexes with alkynes. The efficacy of this strategy was established with the conversion of bromide 1a (R-1 = Me, R-2 = H) to the biaryl phenol 3a (R = Me, R-L = Pr, R-S = H) via the carbene complex 2a. Bromide 1b (R-1 = t-Bu, R-2 = OMe) was then used for the analogous preparation of the diast ereomeric allocolchicinoids 3b (R = Me, R-L = Pr, R-S = H).