Intramolecular Nicholas Reactions in the Synthesis of Dibenzocycloheptanes. Synthesis of Allocolchicine NSC 51046 and Analogues and the Formal Synthesis of (-)-Allocolchicine

[摘要]：The preparation of dibenzocycloheptyne-Co-2(CO)(6) complexes by intramolecular Nicholas reactions of biaryl-2-propargyl alcohol-Co-2(CO)(6) derivatives is described. Reductive decomplexation of the dibenzocycloheptyne-Co-2,(CO)(6) complexes affords the corresponding dibenzocycloheptenes, individual members of which have been employed in a,formal total synthesis of (-)-allocolchicine, the preparation of 6,7-dihydro-3,4,9,10,11-pentamethoxy-5H-dibenzo[a,c]cyclohepten-5-one, and the enantioselective total syntheses of NSC 51046 and its 3,8,9,10-tetramethoxy regioisomer.

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