Functionalization of spirocyclopentadienes using organomolybdenum reagents: approaches to the synthesis of (±)-silphinene

Abstract

(η5-Indenyl)molybdenum dicarbonyl complexes of 1,3-dienes, including spirocyclopentadienes, can be cleanly prepared from stoichiometric amounts of 1,3-dienes and [(η5-indenyl)Mo(CO)2(CH3CN)2][BF4] (1) in dichloromethane solution. Nucleophilic addition of lithium dimethylcuprate to the complexed diene occurs in the expected manner to provide η3-allylmolybdenum complexes in high yield. Applications of this chemistry towards the synthesis of (±)-silphinene are described. The allylmolybdenum complexes [(η5-C9H7)(η3-C10H15)Mo(CO)2] (8) and [(η5-C9H7)(η3-C15H23)Mo(CO)2] (33) were structurally characterized by X-ray crystallography. Compound 8: space group P21/n with a = 9.393(1) Å, b = 10.469(2) Å, c = 17.704(2) Å, β = 91.05(1)°, Z = 4, and V = 1770.5(4) Å3. Compound 33: space group P21/c with a = 17.616(4) Å, b = 7.688(2) Å, c = 15.873(2), β = 90.12(2)°, Z = 4, and V = 2149.7(6) Å3.