REACTION OF CHROMIUM (FISCHER) CARBENES AND SULFILIMINES

The photochemical reactions of alkoxychromium (Fischer) carbenes and sulfilimines lead to imidates in fair to excellent yields. Aromatic, heteroaromatic, and alkylsulfilimines, the latter bearing functional groups such as cyano, sulfone, ether, ester, and dioxolane groups, gave the corresponding imidates in good to excellent yield. However, acyl- and sulfonyl-substituted sulfilimines did not react with chromium carbenes, except for sulfilimines bearing ethoxycarbonyl and phtalimidylamino groups. A variety of differently substituted chromium carbene complexes bearing alkyl, cycloalkyl, styryl, allyl, and alkynyl groups attached either at the carbene carbon or at the oxygen also gave imidates in good yields. For alpha,beta-unsaturated carbenes, the exclusive 1,2-addition of the sulfilimine nitrogen was observed at room temperature, in contrast to the behavior of other nitrogen nucleophiles which are reported to add in 1,4-fashion under these reaction conditions. In turn, optically active imidates of the type ArN=C(OR*)Me [R* = chiral substituent derived from (R)-(+)-1-phenyl-1-butanol, l-(-)-menthol, (1S)-endo-(-)-borneol, and (1R)-(-)-myrtenol] can be prepared efficiently by utilizing the corresponding chiral alkoxy group on the earbene moiety. The reactions above also occur in the dark but reaction times are considerably longer. N-Halosulfilimines reacted with alkoxychromium carbenes to yield N-acylsulfilimines instead of the expected N-haloimidates. Based upon a set of thermal and photochemical reactions between N-haloimidates and diphenyl sulfide in the absence of chromium complexes, the complex (CO)5CrNCMe is proposed to be responsible for this novel reaction of N-haloimidates and diphenyl sulfide.