Access to [6.4.0]Carbocyclic Systems by Tandem Metathesis of Dienynes. A Step toward the Synthesis of a PreD3−D3 Transition State Analogue
摘要:
A new approach to the synthesis of linearly fused 6-8-6 tricarbocyclic systems, tandem ring-closing metathesis of dienynes, allows access to compounds with a carbon framework analogous to the proposed transition state of the isomerization of previtamin D-3 to vitamin D-3.
Intramolecular Pauson–Khandreaction of various alkynyl exo-alkylidene-cyclohexanes and -pentane gives angular type 6–5–5 and 5–5–5 tricyclic compounds in good to high yield. The present reaction also offers convenient construction of two contiguous quaternary centers, which could not be synthesized from alkynyl endo-cycloolefins. Scope and limitation of the present reaction of various exo- and endo-cyclic