ABSTRACT3-Methyl vinyl aziridine undergoes a mild MgI2-promoted SN2' ring-opening and concomitant cyclization with fumarate Michael acceptors to give tri-substituted pyrrolidines. The process is efficient and highly diastereoselective. This methodology has been applied to a concise asymmetric synthesis of (+)-allo-kainic acid.
Convenient accesses to enantiomerically pure 2-, 2,3-, 2,6-, 2,3,6-substituted piperidines and 1,4-substituted indolizine are described. At first, indium-mediated aminoallylation and -crotylation of aldehydes with (R)-phenylglycinol or (1R,2S)-1-amino-2-indanol gave homoallylamines with high stereocontrol. Then, these products, submitted to a Rh(I)-catalyzed hydroformylative cyclohydrocarbonylation, afforded perhydrooxazolo[3,2-a]piridines whose oxazolidines are opened with nucleophiles. Finally, the removal of the chiral auxiliaries delivered the enantiomerically pure piperidines.
The novel rhodium complex [Rh(S)-PhanephosA C H T U N G T R E N N U N G (cod)]-catalyzed hydrogenation of disubstituted (E)-enol acetate carboxylic acids is reported. The catalytic cycle works under 30 bar of hydrogen under conventional heating giving different 3acetoxy-2,3-disubstituted carboxylic acids with ee ! 90%. Hydrogenation occurred also under microwave dielectric heating without eroding the enantioselectivity but improving the overall efficiency of the process. With microwaves, hydrogen pressure and reaction time required for complete hydrogenation dropped to 5 bar and 30 min, respectively. The best performance of this catalyst under microwave irradiation was TON 100, TOF 196 h À1 with ee 99% on a 6-g scale.
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