Michael addition of nitroalkanes to nonactivated α,β-unsaturated δ-thiolactams: reactivity, diastereoselectivity, and comparison to α,β-unsaturated δ-lactams

Crystal structure of (2S,4R)-ethyl 4-nitromethyl-1-[(S)-1-phenylethyl]-6-sulfanylidenepiperidine-2-carboxylate

In the title compound, C₁₇H₂₂N₂O₄S, a thio­piperidine derivative, the piperidine ring has an envelope conformation with the methyl­ene C atom opposite to the C=S bond as the flap. The nitro­methyl substituent is equatorial while the eth­oxy­carbonyl group is axial. The mean planes of the nitro­methyl group, the carb­oxy group and phenyl ring are inclined to the mean plane through the five planar atoms of the piperidine ring [maximum deviation = 0.070 (4) Å] by 56.8 (2), 83.8 (5) and 87.1 (2)°, respectively. There is an intra­molecular C—H⋯O hydrogen bond involving an H atom of the eth­oxy­carbonyl group and a nitro O atom. In the crystal, mol­ecules are linked by C—H⋯O hydrogen bonds, forming chains along [100]. The chains are linked by further C—H⋯O hydrogen bonds, forming corrugated layers lying parallel to (001).

Cooperative activation of alkyne and thioamide functionalities; direct catalytic asymmetric conjugate addition of terminal alkynes to α,β-unsaturated thioamides

A detailed study of the direct catalytic asymmetric conjugate addition of terminal alkynes to α,β-unsaturated thioamides is described. A soft Lewis acid/hard Brønsted base cooperative catalyst, comprising [Cu(CH(3)CN)(4)]PF(6), bisphosphine ligand, and Li(OC(6)H(4)-p-OMe) simultaneously activated both substrates to compensate for the low reactivity of copper alkynylide. A series of control experiments revealed that the intermediate copper-thioamide enolate functioned as a Brønsted base to generate copper alkynylide from the terminal alkyne, thus driving the catalytic cycle through an efficient proton transfer between substrates. These findings led to the identification of a more convenient catalyst using potassium hexamethyldisilazane (KHMDS) as the Brønsted base, which was particularly effective for the reaction of silylacetylenes. Divergent transformation of the thioamide functionality and a concise enantioselective synthesis of a GPR40 receptor agonist AMG-837 highlighted the synthetic utility of the present catalysis.

Enantioselective synthesis of a GPR40 agonist AMG 837 via catalytic asymmetric conjugate addition of terminal alkyne to α,β-unsaturated thioamide

A concise enantioselective synthetic route to a potent GPR40 agonist AMG 837 is described. The crucial catalytic asymmetric conjugate addition of terminal alkyne was promoted by a soft Lewis acid/hard Brønsted base cooperative catalyst, allowing efficient construction of the requisite stereogenic center. The thioamide functional group is key to both activation in asymmetric alkynylation and facile transformation into carboxylic acid.