Pergamon S0040-4039(96)0053 l-X Tetrahedron Letters, Vol. 37, No. 19, pp. 3235-3238,1996 Copyright © 1996ElsevierScienceLtd Printed in Great Britain. All rights reserved 0040-4039/96 $15.00 + 0.120 Carbenes in Constrained Systems. 4: Encapsulation of an Asymmetric Diazirine: Reactivity of 2-Methylcyclohexanylidene Murray G. Rosenberg, Steven M. Kam and Udo H. Brinker" Department of Chemistry, State University of New York at Binghamton, Binghamton, NY 13902-6016 USA Abstract: 2-Methyleyclohexanylidene was generated from the corresponding diazirine within the cavities of ct-, 13- and y-cyclodextnn by photolysis in the solid state. To surmise how these constrained systems affect the residing carbene's selectivity, a comparison with conventional reaction methods was made Copyright © 1996 Elsevier Science Ltd Carbenes are highly reactive intermediates that often frustrate efforts to steer which reaction pathway they follow. Thus, it is difficult to eonlrol which intramolecularly-derived isomer the carbene will prefer to rearrange to.' Furthermore, azine formation is always a pertinent option for a freely diffusing carbene or azi-/diazo- precursor) N~_.~- N 1 4 N~N * 3 8 ~'~ ~ 1t 6 5 9 Scheme 1. Some intra- and intermolecular reactions of 2-methylcyclohexanylidene (2). We have shown, 3 however, the ability of molecular host media to alter the selectivity of carbenes. Not only can intermoleeular azine formation be suppressed but certain intramolecular C-H insertions can be enhanced by 3235