Chiral sulfamate esters

Highlighting the synthetic utility of this methodology, the group of Du Bois reported a three step synthesis of the amino acid (K) ( > isoleucine starting from the chiral sulfamate ester 11. Oxidative cyclization with retention of stereochemistry and a simple Cbz protection hydrolysis oxidation sequence provided the amino acid (Scheme 12.11) [17]. 

In addition to epoxides, three-membered nitrogen heterocycles, aziridines, can be obtained by means of catalytic asymmetric aziridinations (Eq. 30). To this aim, chiral ruthenium(salen) complexes 67 [56] and 68 [57] were useful (Fig. 1). The former phosphine complexes 67 gave the aziridine from two cy-cloalkenes with 19-83% ee [56]. On the other hand, terminal alkenes selectively underwent aziridination in the presence of the latter carbonyl complex 68 with 87-95% ee [57]. In these examples, N-tosyliminophenyliodinane or N-tosyl azide were used as nitrene sources. Quite recently, catalytic intramolecular ami-dation of saturated C-H bonds was achieved by the use of a ruthenium(por-phyrin) complex (Eq. 31) [58]. In the presence of the ruthenium catalyst and 2 equiv iodosobenzene diacetate, sulfamate esters 69 were converted into cyclic sulfamidates 70 in moderate-to-good yields. 

In addition to stereospecific insertion into methine C H bonds, When ef al. have demonstrated that excellent stereoinduction can be achieved in the cyclization of branched sulfamate esters. A chair like transition state with an equatorial C H insertion of the metallonitrene is proposed and this stereochemical model explains the syn selectivity observed for the a branched substrate and the anti selectivity for the p branched case (Scheme 12.12) [52]. In contrast, a and P branched chiral... 

Investigations by both Katsuki and Che have highlighted the application of chiral Mn(III) salen complexes for asymmetric N-atom transfer reactions (Fig. 17) [79-81]. In the former case, the use of [Mn(salen)PF6] together with PhI= Ts affords modest product yields and enantiomeric ratios for amination of simple benzylic and allylic starting materials. A high-valent Mn imido species is presumed to be the active oxidant. Methodological and mechanistic studies conducted by Che have found that the same types of Mn(III) salen complexes will induce oxidative cyclization of sulfamate esters. Although these catalysts afford... 

Espino et al. reported that the oxidative cyclization of the sulfamate esters 740 with PhI(OAc)2, in the presence of Rh2(OAc)4, gave the heterocycles 741, which had both S—O and S—N bonds in the ring, in high yields (Scheme 228).300b The oxidative cyclization of chiral 742 gave 743 in 91% yield with perfect stereocontrol, which was converted to R)-j3-isoleucine 744 (Scheme 229). 

Wehn et ah have also reported the intramolecular aziridination of chiral homoallyl sulfamate esters, sueh as 216, with moderate selectivity. The bicyelie... 

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