Explosion hazard in asymmetric cyclopropanation

André B. Charette
University of Montreal, Quebec

Chemical & Engineering News (6 Feb 1995) Vol. 73, No. 6, pp. 2.

SIR: It can be dangerous to scale up the asymmetric Simmons-Smith cyclopropanation of allylic alcohols that we recently reported [J. Am. Chem. Soc.,116, 2186, (1994)]. Most of the cyclopropanation reactions reported in the original communication were carried out on a 0.5-mmol scale. Recently, in our laboratories, violent explosions occurred on two occasions when we attempted to use the procedure on an 8-mmol scale. In one case, the explosion occurred while generating the bis(iodomethyl)zinc reagent; on the other occasion, it occurred when the alcohol-chiral ligand mixture was added to the preformed reagent.

I would, therefore, recommend that this procedure never be used on scales above 1 mmol. A safer procedure, which was tested up to the 0.1-mol scale, gave comparable yields and enantioselectivities; a description of it will appear shortly in the Journal of Organic Chemistry.

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