N 2 -Sulfonyl-α-diazo amidines can be synthesized by the reaction of electron rich alkynyl amines with electron poor sulfonyl azides through 1,3-dipolar cycloaddition that proceeds with perfect regioselectivity. In the presence of rhodium(II) carboxylate catalysts, denitrogenation occurs to give the corresponding metallocarbene but there are then two competing processes: 1,2-H shift and O-transfer from the sulfonyl group to the metallocarbene center. The outcome can be controlled using an electron poor nitrobenzenesulfonyl group and large carboxylate rhodium ligands to select for 1,2-H shift, forming α,β-unsaturated amidines in high yield and with excellent Zselectivity.
Heating unsaturated N2-sulfonyl amidines with BF2OTf in acetonitrile transformed them into stereodefined cyclic amidines. Investigating by-products of the reaction suggested a fascinating mechanism including 1,7-H shift and electrocyclisation.
Abstract1,1-Dibromoalkenes can be used as direct precursors to three classes of 5-substituted 1,2,3-triazoles. Three different approaches to 1,2,3-triazole products were developed, linked to the N1-substituent. Treatment of 1,1-dibromoalkenes with n-butyllithium and reaction with a sulfonyl azide gave 5-substituted 1-sulfonyl-1,2,3-triazoles. The use of lithium base followed by transmetalation to zinc and reaction with aryl azides allowed access to 1-aryl-1,2,3-triazoles. Finally, the use of EtMgBr as base and reaction with an alkyl azide formed 1-alkyl-1,2,3-triazoles.
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