A new route to hindered tertiary amines

The Rh(2)(OAc)(4)-stabilized carbenoid derived from dimethyl diazomalonate has been found to insert into the N-H bond of sterically hindered secondary aliphatic amines to afford hindered tertiary aliphatic amines in quite satisfactory yields. For example dimethyl 2-(dicyclohexylamino)propanedioate was formed in 85% yield from dicyclohexylamine, and the severely hindered dimethyl 2-(2,2,6,6-tetramethyl-1-piperidinyl)propanedioate was formed in 38% yield from 2,2,6,6-tetramethylpiperidine. The Rh(2)(OAc)(4) - dimethyl diazomalonate reaction was found to work also for arylalkylamines and diarylamines. In these cases, small amounts of products resulting from formal insertion of the carbenoid into an aromatic C-H bond were detected. Substitution at ortho positions caused the yield of C-H insertion products to increase. Other diazo compounds, viz. ethyl diazoacetoacetate, 2-diazocyclohexane-1,3-dione, and 2-diazo-5,5-dimethylcyclohexane-1,3-dione, performed satisfactorily in Rh(2)(OAc)(4)-catalyzed reactions with arylalkylamines and diarylamines, but led to complicated reaction mixtures with dialkylamines.