NEW METHODOLOGIES FOR THE ASYMMETRIC SYNTHESES OF AMINES AND NITROGEN HETEROCYCLES FROM ENANTIOPURE SULFINIMINES (N-SULFINYL IMINES)

Abstract

The objective of this research was to development new methodologies for the asymmetric syntheses of amine and natural products from enantiopure sulfinimines (N-sulfinyl imines). In this context, new methods was devised for the asymmetric synthesis of 2,5-cis and trans-disubstituted pyrrolidines from 3-oxo pyrrolidine 2-phosphonates, prepared by an intramolecular metal carbenoid N-H insertion from a sulfinimine derived delta-amino-alpha-diazo- beta-ketophosphonate. Horner-Wadsworth-Emmos reaction of the 3-oxo pyrrolidine 2-phosphonates and aldehydes provided pyrrolidine enones. Hydrogenation (Pd/H2) of the pyrrolidine enones gave cis-2,5-disubstituted pyrrolidines. Luche reduction the pyrrolidine enones followed by a TFA-NaBH3CN mediated hydroxy directed reduction provided the 2,5-trans products. (+)-Preussin, a potent antiviral and antitumor agent was prepared in 9 steps in 28% overall yield from the sulfinimine. An acid catalyzed intramolecular Mannich cyclization of a sulfinimine-derived N-sulfinyl syn-alpha-methyl-beta-amino ketones was employed for the asymmetric synthesis of 2,3,5,6-tetrasubstituted piperidinones. The beta-amino ketones were prepare by treatment of prochiral lithium Weinreb amide enolates with enantiopure (E)-N-(4-(benzyloxy)butylidene)-2,4,6-triisopropylbenzenesulfinamide. This new methodology was highlighted in the first asymmetric synthesis of the poison frog alkaloid (-)-indolizidine 221T. By manipulation of water concentration in tetrahydrofuran, syn- and anti-2,3-diamino esters were prepared by treatment of the lithium enolate of N-(diphenylmethylene) glycine ethyl ester with sulfinimines. Anhydrous THF afforded enantiopure syn-2,3-diamino esters with a syn/anti selectivity of better than 25:1. In a THF-H2O the anti-2,3-diamino esters were formed. The mechanism involves the generation of H2O-LDA species in the formation of enolate which inhibited the retro-Mannich fragmentation in the diamino ester species. (SR,2S,3R)-(-)-Ethyl-2-(N,N-dibenzylamino)-3-N-(p-toluenesulfinyl)amino-pent-4-enoate was employed in an improved total synthesis of the anti-tumor antibiotic (-)-agelastatin A. A series of N-sulfinyl aza-Morita-Baylis-Hillman products were prepared by addition of vinylaluminum and N-methylmorpholine-N-oxide reagents to enantiopure N-(p-toluenesufinyl)- and N-(2-methypropanesulfinyl)-derived sulfinimines from the least hindered direction via a non-chelation control mechanism. Hydrogenation of the these acrylates with a rhodium(I) catalyst afforded anti-alpha-substituted-beta-amino esters with a anti/syn selectivity of better than 17:1. This new methodology is useful for the asymmetric synthesis of anti-alpha-alkyl-beta-amino esters, which are valuable chiral building blocks for the preparation of biologically active nitrogen-containing natural products.