Dirhodium -catalyzed sulfamate

The search for an efficient and versatile dirhodium-catalyzed asymmetric C(sp )-H amination reaction is an issue for which there is stiU ample room for improvement. The field was pioneered again by Muller who had designed chiral rhodium(II) complexes for inter- and intramolecular reactions, though with limited success as the ees did not exceed 66%. " With respect to the catalytic asymmetric intramolecular nitrene C(sp )—H insertion, the best results reported so far have been obtained with the rhodium(II) carboxamidate species Rh2(S-nap)4 This complex affords the corresponding cyclic sulfamates with excellent ees (ees enantiomeric excesses) of up to 99% (Scheme 32). However, the scope is limited to benzyhc substrates as, despite the excellent chemoselectivity, the ees remain below 84%... 

A recent DFT study has shown that retention of configuration observed for the above reactions is in agreement with the insertion of singlet nitrene and a concerted product formation [150 is the transition state for the reaction shown in Equation (6.135)]. Du Bois and coworkers have performed detailed mechanistic investigations of the intramolecular sulfamate ester C-H amination reaction catalyzed by a dirhodium complex. Reactivity patterns, Hammett analysis, and kinetic isotope effect studies have provided support for the concerted, asynchronous transition structure 151. A similar conclusion was arrived at for an analogous intermolecular process. ... 

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