Asymmetric Michael addition reactions using ethyl (S)-4,4-dimethylpyroglutamate as a chiral auxiliary

Diastereoselective and enantioselective conjugate addition reactions utilizing α,β-unsaturated amides and lactams

The conjugate addition reaction has been a useful tool in the formation of carbon-carbon bonds. The utility of this reaction has been demonstrated in the synthesis of many natural products, materials, and pharmacological agents. In the last three decades, there has been a significant increase in the development of asymmetric variants of this reaction. Unfortunately, conjugate addition reactions using α,β-unsaturated amides and lactams remain underdeveloped due to their inherently low reactivity. This review highlights the work that has been done on both diastereoselective and enantioselective conjugate addition reactions utilizing α,β-unsaturated amides and lactams.

Chemoselective Nucleophilic Attack on N-Acyl Derivatives of (S)-Ethyl 4,4-Dimethyl Pyroglutamate (DMPG)

[reaction: see text] Heteronucleophiles and C-nucleophiles chemoselectively react with N-acyl (S)-ethyl 4,4-dimethyl pyroglutamate (DMPG) affording esters, amides, and ketones in high yield. The intramolecular process allows the stereoselective formation of beta-hydroxy acids likely by formation and ring opening of the corresponding beta-lactones

Pseudoephedrine as a chiral auxiliary for asymmetric Michael reactions: synthesis of 3-aryl-delta-lactones

[reaction: see text] The asymmetric Michael reaction of pseudoephedrine amides is reported. The 1,5-dicarbonyl products are converted to 3-aryl-delta-lactones in a two-step reduction/lactonization sequence. This method provides access to enantiomerically enriched trans-3,4-disubstituted delta-lactones.

1,6-Asymmetric induction during the conjugate addition of arylcopper reagents to a chiral sulfinyl-substituted pyrrolyl alpha,beta-unsaturated amide

The asymmetric conjugate addition of arylcopper reagents derived from aryl Grignard reagents and copper(I) iodide to a chiral 1-[2-(p-tolylsulfinyl)]pyrrolyl cinnamide proceeded smoothly to give (3R)-adducts with high diastereoselectivities (> or =92% de) in high yields. Conjugate additions either of the cinnamide with the alkyl Grignard reagent-copper(l) iodide combination or of the crotonamide derivative with aryl Grignard reagent-copper(l) iodide gave moderate to good diastereoselectivities. With these sulfinyl pyrrolyl alpha,beta-unsaturated amides, the chiral auxiliary was efficiently recovered without any loss of optical purity after asymmetric conjugate addition.

Enantioselective synthesis of peperomins A, C, D, and analogs — Examination of diastereoselective cuprate conjugate additions to N-enoyl-4-diphenylmethyl-2-oxazolidinones

A concise and general route to secolignans has been developed. The first total synthesis of secolignans peperomin A (1a), peperomin C (1b), and peperomin D (1c) was accomplished in ~28% overall yield over five synthetic steps. Peperomin analogs (1d) and (1e), possessing two differentially substituted aryl groups, were synthesized by a highly selective conjugate addition. The overall yield for the analogs 1d and 1e were 27 and 26%, respectively.Key words: peperomins, secoliganans, conjugate additions, 4-diphenylmethyl-oxazolidin-2-one.

Highly diastereoselective 1,4-addition of an organocuprate to methyl alpha-D-gluco-, alpha-D-manno-, or alpha-D-galactopyranosides tethering an alpha,beta-unsaturated ester. Novel asymmetric access to beta-C-substituted butanoic acids

The 1,4-addition of magnesium divinylcuprate prepared from vinylmagnesium bromide and cuprous bromide to some 4-O-crotonyl derivatives of methyl alpha-D-glucopyranoside proceeds with a high level of diastereochemical induction, providing the adduct in good-to-excellent yields. Other organocuprates also serve as effective carbon nucleophiles for the 1,4-addition. Removal of the carbohydrate moiety from each adduct afforded a variety of beta-C-substituted butanoic esters in remarkable enantiomeric excess. The 1,4-addition of the same cuprate to some methyl alpha-D-manno- or alpha-D-galactopyranosidic substrates in which a crotonyl group was incorporated, each at 3-OH, was also investigated. The reverse pi-facial attack of the cuprate was observed when some D-manno-type substrates were subjected to 1,4-addition conditions similar to those used for the D-gluco-type substrates. Furthermore, some D-galacto-type substrates provided 1,4-adducts with higher diastereoselectivities.