A Novel Asymmetric Route to Chiral, Nonracemic cis-2,6-Disubstituted Piperidines. Synthesis of (+)-Pinidinone and (+)-Monomorine

Asymmetric synthesis of 1,3-aminoketals

“…Thus, the two benzylic groups of amides 2 were cleaved by hydrogenolysis in the presence of PearlmanÕs catalyst 18 and amines 10 thus obtained were used in the reaction without further purification, with benzyl chloroformate under Schotten-Bauman conditions. 19 Amides 11 were thus obtained in two steps in yields of up to 70%. At this stage, the transformation of Weinreb amides 11 into ketones by the use of a Grignard reagent, 12,15 a critical key step of the synthetic pathway, was tested (Scheme 6).…”

Diastereoselective preparation of cyclic β-aminoketals. Application to the total synthesis of piperidine alkaloids

“…Hydrogenolysis of the α-methylbenzyl group of 16 with palladium on charcoal in the presence of ammonium formate furnished piperidine 24, which, without further purification, was immediately reprotected with benzyl chloroformate. 19 By this route, piperidine 25 was obtained in two steps with a 70% overall yield after purification. …”

Asymmetric processes

“…66 cis-2,6-Disubstituted piperidines have been prepared from Meyers' chiral bicyclic lactams by an Eschenmoser sulfur contraction followed by stereoselective hydrogenation. 67 The sulfinamide 46 has been used to introduce a sulfoxide auxiliary by reaction with enolates of ketones (Scheme 15). 68 The auxiliary is used to direct the reduction of the ketone, and can then be eliminated thermally to give chiral allylic alcohols or their esters.…”