Abstract
The η 3 -allymolybdenum complexes [Mo(C 5 H 5 )(CO) 2 (syn-1-C 3 H 4 R)] (R = vinyl or buta-1,3-dienyl) undergo BF 3 catalysed carbon-carbon bond formation with aldehydes, ketones and α,β-unsaturated ketones; applications to the synthesis of functionalized 1,3-dienes and 1,3,5-trienes are reported, and evidence for formation of an s-trans-diene as an intermediate is presented.