3 aldehyde because of the following limitations:(i) low reactivity of the geminal dimetallic compounds (Mtl= BS or AI6);(ii) lack of stereoselectivity of the products; 5bs6c (iii) side reactions such as the reduction of a carbonyl group'or reductive coupling of an aldehyde to al, 2-dioL7 Recently, Knochel and Normant reported that 1-magnesium 1-zinc compounds add to aldehydes with the assistance of BF3. 0Et2 to give olefins with good E selectivity. 8 ...