Diastereo- and Enantioselective Synthesis of Carbocyclic and Heterocyclic β-Amino Acids by Tandem Aza Michael Addition/Intramolecular Cyclization

Diastereoselective Synthesis of trans-β-Amino Cyclohexyl Ketones and trans-3-Amino-4-acyl-tetrahydropyrans from Intramolecular C-Alkylation of ω-Halo-Substituted β-Sulfinamido Ketones

Reaction of ω-halo-substituted nonracemic β-sulfinamido ketones with NaH afforded the β-amino cyclohexyl ketones in excellent yields and diastereoselectivity, via an intramolecular C-alkylation, α to the carbonyl group. The reaction was found to be general and can be applied for the synthesis of different cyclohexyl amino ketones and tetrahydropyrans possessing amine and acyl substitutions.

Cyclic beta-amino acid derivatives: synthesis via lithium amide promoted tandem asymmetric conjugate addition-cyclisation reactions

The product distribution upon conjugate addition of homochiral lithium N-benzyl-N-alpha-methylbenzylamide to dimethyl-(E,E)-nona-2,7-dienedioate can be controlled to give either the cyclic 1,2-anti-1,6-anti-beta-amino ester (derived from conjugate addition and intramolecular enolate cyclisation) or the acyclic bis-beta-amino ester derivative (derived from double conjugate addition) in high de. The introduction of a protected nitrogen functionality into the diester skeleton facilitates, after conjugate addition and intramolecular enolate cyclisation, the asymmetric construction of piperidines in high de; variation in the N-protecting group indicates that the highest stereoselectivity is observed with alpha-branched N-substituents. Tandem conjugate addition-aldol reactions can also be achieved stereoselectively, with lithium amide conjugate addition to epsilon- and zeta-oxo-alpha,beta-unsaturated esters giving the corresponding five and six membered cyclic beta-amino esters in high de. N-deprotection by hydrogenolysis of the products arising from these reactions furnishes a range of polyfunctionalised transpentacin and transhexacin derivatives in high de and ee.