Chirality transfer pyrrolidine

Chiral amines can be prepared by asymmetric hydrogenation, transfer hydrogenation and hydrosilylation of imines. The piperidine 137 with 98% ee was obtained by highly efficient asymmetric hydrogenation of the cyclic imines 136 catalysed by the Ti catalyst 61 [82]. Pyrrolidine 139 with 99% ee was obtained in 34% after 50%... 

The reaction of (—)-151 with imines such as 2-methyl-l-pyrrolidine illustrated in Scheme 33 affords complex 222. An X-ray structure of 222 shows that the coordinated imine is oriented perpendicular to the 1,2-azaborolyl ring. This orientation which contrasts with that assumed for 219 must be due to the greater steric bulk of the imine. Reaction of 222 with allylmagnesium bromide gives 223 with excellent stereoselectivity. Hydrolysis affords the free amine 224. The reactions illustrated in Schemes 32 and 33 demonstrate that 1,2-azaborolyl iron complexes can efficiently transfer chirality to B-bound organic substrates. The development of catalytic versions of these stoichiometric reactions would be a highly desirable extension of this work. 

A conjugate addition and trapping strategy has emerged as a viable method for forming a chiral center a to a carbonyl by diastereoselective hydrogen atom transfer after initial radical addition to an acrylate. An example shown in Eq. (13.22) uses a C-2 symmetric pyrrolidine chiral auxiliary to induce facial selectivity in the hydrogen atom transfer step [32]. This particular example afforded 89% yield and 25 1 preference for 74. 

Chiral oxazaphosphorinanes, derived from (-)-8-amino menthol are alkylated with good to excellent diastereoselectivities. The regioselectivity in the alkylation is dependent on the base used for protonation.Both enantiomers of the major diastereoisomer of 2-(l-phenyl)ethylamino-4-thioxo-4-phenoxy-l,3,4-thiazaphos-phol-2-ine were obtained in optically pure form by the reaction of 0-phenyl(chloro-methyljisothiophosphonate with (i )-(-l-)- and (5)-(—)-(l-phenyl)ethylamine. Phase-transfer 7V-allylation and A7-propargylation of (bicyclo[1.1.0]butylmethyl)-amines initiate diastereoselective pericyclic cascade reactions that culminate in novel spirocyclic (206) and tricyclic pyrrolidine (207) heterocycles through formal ene or [2 + 2] pathways (Scheme 76). ... 

Full details are now available of the application of the L-proline-derived pyrrolidine (22) as ligand in the asymmetric addition to aldehydes of alkyl-lithiums (45—95% optical yields) and dialkylmagnesiums (22—92% optical yields). Modification of lithium (and sodium) tetra-alkylaluminates with the chiral amino-alcohols (-)-N-methylephedrine (13), quinine, and cinchonine (Scheme 10) produces reagents (23) that have been shown to give asymmetric alkyl transfer... 

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