Asymmetric intramolecular cyclopropanation of diazo compounds with metallosalen complexes as catalyst: structural tuning of salen ligand

Intramolecular cyclopropanation of alkenyl alpha-diazoacetates and alkenyl diazomethyl ketones was examined by using optically active (ON+)Ru(11)(salen) and Co(II)(salen) complexes as catalysts. For the cyclization of 2-alkenyl alpha-diazoacetates, Co(II)(salen) complexes 9 and 10 were found to be superior catalysts to the corresponding (ON+)Ru(11)(salen) complexes 4 and 5. On the other hand, (ON+)Ru(II)(salen) complex 2 was found to be the catalyst of choice for the cyclization of 3-alkenyl diazomethyl ketones, and complex 4 was found to be a good catalyst for the cyclization of (E)-4-alkenyl diazomethyl ketones. The present study demonstrates that metallosalen complexes, especially optically active (ON+)Ru(II)(salen) and Co(11)(salen) complexes, can serve as efficient catalysts for the cyclization of alkenyl diazocarbonyl compounds, if a suitable salen ligand is used as the chiral auxiliary. (C) 2003 Elsevier Science Ltd. All rights reserved.