Rhodium-Catalyzed Diastereoselective Intermolecular C-H Amination

Key words

rhodium - C-H amination - diastereoselectivity

Significance

Over the last few years, metal-catalyzed C-H functionalization has been an area of intense research. In particular, intramolecular amination reactions of saturated C-H bonds represented a powerful tool for the synthesis of chiral nitrogen-containing compounds (for recent examples, see: J.-S. Liang et al. J. Org. Chem. 2004, 69, 3610-3619; M. Kim et al. Org. Lett. 2006, 8, 1073-1076). Herein the first efficient intermolecular version of this reaction is described, using catalytic amounts of chiral rhodium complex[Rh₂{(S)-nttl}₄], substoichiometric amounts of alkane and a combination of PhI(OCOt-Bu)₂ and (S)-N-(p-toluenesulfonyl)-p-toluenesulfonimid­amide to afford the chiral iminoiodane in situ.

Comment

This methodology proved to be superior in many different aspects to the preexisting catalytic methods reported to date. Indeed, both electron-rich and electron-poor C-H bonds as well as allylic substrates (to a smaller extent) are readily and diastereoselectively functionalized. Of particular synthetic utility is the selectivity in the reaction with 2-methoxyindane which gives selectively the trans isomer whereas an intramolecular reaction would have lead to the syn compound. The high selectivity can be explained by a matched effect between the catalyst system and the sulfonimidamide. Interestingly enough, the cleavage of the sulfonimidoyl group could be carried out without loss of the chiral information.