Stable and readily available 1-sulfonyl triazoles are converted to the corresponding imidazoles in good to excellent yields via a rhodium(II)-catalyzed reaction with nitriles. Rhodium iminocarbenoids are proposed intermediates.

Changing the rings: A variety of N‐fused pyrrolo‐ and imidazopyridines can be readily formed by a direct Rh‐catalyzed transannulation of pyridotriazoles with alkynes and nitriles, respectively (see scheme). Substituted pyridotriazoles can also serve as stable precursors for Rh carbenoids, the preparation of which does not require special precautions or slow‐addition techniques.

Rhodium(II) azavinyl carbenes, conveniently generated from 1-sulfonyl-1,2,3-triazoles, undergo a facile, mild and convergent formal 1,3-insertion into N–H and O–H bonds of primary and secondary amides, various alcohols, and carboxylic acids to afford a wide range of vicinally bis-functionalized Z-olefins with perfect regio- and stereoselectively. Utilizing the distinctive functionality installed through these reactions, a number of subsequent rearrangements and cyclizations expand the repertoire of valuable organic building blocks constructed by reactions of transition metal carbene complexes, including α-allenyl ketones and amino-substituted heterocycles.

N-Sulfonyl 1,2,3-triazoles readily form rhodium(II) azavinyl carbenes, which react with olefins to produce cyclopropanes with excellent diastereo-and enantioselectivity and in high yield.Diazocarbonyl compounds 1 are well known precursors to metal carbenes 2 (eq 1). 1 The versatile reactivity of the latter is recognized by numerous synthetic applications. 2 In contrast, related azavinyl carbenes 3 have not been employed in synthesis, 3 primarily due to the limited availability of corresponding α-diazoimines. 4 These reactive intermediates can be viewed as synthetic equivalents of formyl carbenes, in which both amine and aldehyde functions can be revealed by simple transformations, thus significantly expanding the repertoire of chiral molecules that may be accessed via carbene-based synthetic methods. Herein we wish to report a first example of highly diastereo-and enantioselective Rh(II)-catalyzed cyclopropanation employing azavinyl carbenes 3 derived from 1-sulfonyl 1,2,3-triazoles 4. The latter can be obtained using the copper-catalyzed cycloaddition reaction of alkynes with sulfonyl azides. 5 fokin@scripps.edu. Supporting Information Available: Experimental details, characterization data and NMR spectral charts. This material is available free of charge via the Internet at http://pubs.acs.org. Our recent success in the Rh-catalyzed transannulation of N-sulfonyl 1,2,3-triazoles had proven that these easily available, reasonably stable and seemingly unreactive compounds are reliable precursors of azavinyl carbenes. 6 Accordingly, we further explored the Rh(II) catalysis with 1,2,3-triazoles targeting enantioselective transformations. To this end, we examined the cyclopropanation of styrene with 1-sulfonyl-4-phenyl-1,2,3-triazoles 4 in the presence of various chiral Rh(II) complexes 7 (Figure 1) in 1,2-dichloroethane at 80 °C (Table 1). The resulting sulfonyl imine 5 was smoothly converted into the corresponding aldehyde 6a by treatment with K 2 CO 3 in wet methanol. NIH Public AccessFirst, we found that the use of 1-toluenesulfonyl derivative 4a with Rh 2 (S-DOSP) 4 8 catalyst afforded cyclopropane-carboxaldehyde 6a in high yield and excellent transdiastereoselectivity. However, enantioselectivity of the reaction was low (Table 1, entry 1). Next, Rh 2 (S-PTAD) 4 9 and Rh 2 (S-PTTL) 4 10 catalysts were examined, providing 6a with over 70% ee (entries 2 and 3). Increased steric demand of the ligands on rhodium resulted not only in very sluggish reaction, but also in drastic erosion of the diastereoselectivity (entry 4). We hypothesized that switching to a less sterically encumbered carbene precursor might improve the overall performance of the reaction. Indeed, 1-mesyl triazole 4b reacted smoothly in the presence of Rh 2 (S-PTTL) 4 catalyst furnishing the cyclopropane product with 88% ee (entry 5). To our great delight, Rh 2 (S-NTTL) 4 ,11 in combination with sulfonyl triazole 4b allowed for excellent enantioselectivity (96% ee) and yield, 95% (entry 6). Remarkably, n-octylsulfonyl and isopropylsulfonyl t...