Abstract
The compound CpMo(CO) 2 (η 3 -vinylallyl) (5) underwent a novel cyclization with TCNE and PhCHO (BF 3 -catalyzed) in CH 2 Cl 2 to afford a six-membered ring product Treatment of 5 with PhCHO/BF 3 ·Et 2 O in benzene yielded a Mo–η 4 -trimethylenemethane salt, generated from the electrophilic addition of PhCHO to the vinyl group of 5. Characterization of this cation has been achieved by IR and 1 H NMR spectra and by its subsequent reaction with NaBH 3 CN and R 2 CuLi (R = Ph, PhC≡C). Formation of this trimethylenemethane cation is also observed for a similar BF 3 -catalyzed reaction between methyl vinyl ketone and acetone in benzene. The synthetic utility of this carbon–carbon-forming reaction in organic synthesis has been investigated and is described. © 1992, American Chemical Society. All rights reserved.