Amine rearrangement, chirality

The alkaloid (+)-pinidine81 (4) is obtained as a single a s-stereoisomer in a one-pot transformation of the chiral methyl sulfide 3 via oxidative amination, rearrangement, intramolecular imine formation and stereoselective reduction. 

Since 1980, the applications zeolites and molecular sieves in the speciality and fine chemicals increased enormously. Zeolites are being used in the various types of reactions like cyclization, amination, rearrangement, alkylation, acylations, ammoxidation, vapour and liquid phase oxidation reactions. Zeolites and molecular sieves have also been used to encapsulate catalytically active co-ordination complexes like ship-in-bottle and as a support for photocatalytic materials and chiral ligands. Redox molecular sieves have been developed as an important class of liquid and vapour phase oxidation and ammoxidation reactions. We have discussed few typical recent examples of various types of reactions. 

The rearrangement of ammonium ylides 27 derived from chiral amines affords chiral 3-butenals 28 in modest yield120. Critical to the observed diaslereoface selectivity of the rearrangement is the substrate-directed alkylation of amines 26 to afford asymmetric ammonium salts. The observed asymmetric induction is consistent with rearrangement through a transition state conformation in which the more substituted carbon (RL) of the auxiliary occupies an exo orientation. 

Sulfides can be oxidized to sulfoxides by reaction with NCS in methanol (0°C, 1 h). Similarly, selenides couple with amines when activated by NCS to form selenimide species. These have been generated from allylic selenides in order to prepare allylic amines and chiral secondary allylic carbamates by [2,3]-sigmatropic rearrangement (eq 8). ... 

Similarly, but in the cyclic series, the thio-Claisen rearrangement of substrates derived from chiral thiolactams was reported to be facile but poorly stereoselective [129]. The low stereocontrol observed in both cases may be explained by the lack of facial selectivity resulting from the free rotation around the C-N bond of the N,S-ketene acetals. This critical issue has been solved either by constructing a rigid bicyclic framework or by using C2-symmetric amines as chiral inductors. The former strategy, developed by Meyers et al. [45], involved bicycUc thiolactams, which were transformed into N,S-ketene acetals by deprotonation with LDA, followed by S-allylation with various allyl halides (Scheme 9.27). 

Cohen F, Overman LE (1998) Planar-chiral cyclopalladated ferrocenyl amines and imines as enantioselective catalysts for allylic imidate rearrangements. Tetrahedron Asymmetry 9 3213-3222... 

Overman LE, Owen CE, Pavan MM, Richards CJ (2003) Catalytic asymmetric rearrangement of allylic N-aryl trifluoroacetimidates. A useful method for transforming prochiral allylic alcohols to chiral allylic amines. Org Lett 5 1809-1812... 

Imidate esters can also be generated by reaction of imidoyl chlorides and allylic alcohols. The lithium anions of these imidates, prepared using lithium diethylamide, rearrange at around 0°C. When a chiral amine is used, this reaction can give rise to enantioselective formation of 7, 8-unsaturated amides. Good results were obtained with a chiral binaphthylamine.265 The methoxy substituent is believed to play a role as a Li+ ligand in the reactive enolate. 

An alternative synthesis producing a chiral-substituted 3-azoniaspirooctane, 153 has been published by Liu and co-workers where a modification of the Payne rearrangement was applied to amine epoxide 152 (Equation 35) <1997JCS(P1)511>. 

In order to obtain stereoselective formation of the chiral centers C-3, C-7, and C-14, we explored the use of chiral derivatives of our indoloaze-pine 153. Earlier, we had already found that the A(-benzylindoloazepine ester 215 rearranged on heating to an a-methylene lactam 216, indicating the possibility of thermal generation of an intermediate secondary amine indoloacrylate 217. It was also found that this intermediate could be trapped with a variety of aldehydes. Thus, D-seco D-E-trans vincadiffor-mine congeners (218) could be obtained by condensation of the indoloaze-pine 215 with aldehydes at 100°C (Scheme 54) (132). Consequently, introduction of a chiral substituent onto N of the indoloazepine 153 prior to condensation with our 4-ethyl-4,5-dihydroxypentanal acetonides 186 and 187 appeared to be an option for chiral induction in the formation of cen-... 

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