A series of five- to nine-membered nitrogen-containing heterocycles were prepared via a general and efficient sequence featuring rhodium-catalyzed insertions of α-diazocarbonyls into the N-H or C-H bonds of a series of tert-butoxy-(Boc)-protected amines, followed by ring-closing metathesis catalyzed by ruthenium benzylidene complexes. The newly developed methodology allows easy and convenient access to highly functionalized azacycloalkenes in good yields and excellent selectivities.
Vinyl diazoacetoacetate and styryl diazoacetate were found to undergo exceptionally chemoselective carbenoid insertions into the N-H bonds of a series of Boc-protected amines in good yields; however, no stereoselectivity was observed for this process. In contrast, diastereo- and enantioselective C-H insertions and cyclopropanations were observed for the decomposition of styryl diazoacetate catalyzed by the same rhodium catalyst. Based on these findings, reactivity trends of rhodium carbenoids derived from styryl diazoacetate were postulated.