Stereoselective Double Alkylation of Ethyl N-Boc-pyroglutamate

Ethyl 4,4-dimethyl pyroglutamate (DMPG): a chiral auxiliary in cyclopropanation and carbonyl group activator

“…The pyroglutamate derivative 2 used in this study was obtained in an 80% yield by treatment of 1 with n-butyllithium followed by reaction with crotonyl chloride. 16,18 The dimethylsulfonium acetate bromide (EDSA) 19 and …”

“…Our contributions in the field include the diastereoselective cyclopropanation of cyclic and acyclic enones with ethyl dimethylsulfonium acetate bromide, 14 and the stereoselective cyclopropanation of enantiomerically pure dihydroxycyclopentenones for the enantioselective synthesis of 2-aminobicyclo[3.1.0]hexane-2,6-dicarboxylic acid. 15 In the light of our findings with (S)-ethyl 4,4-dimethyl pyroglutamate 1 (DMPG) 16 as an efficient chiral auxiliary in stereoselective aldol condensations 17 and asymmetric Michael addition 18 reactions, it was of interest to explore the behaviour of N-enoyl substrates incorporating DMPG towards an stereoselective cyclopropanation reaction. The DMPG group will not only activate the N-enoyl carbonyl group for the cyclopropanation reaction but also it will provide a means for further functionalization when reacted with an appropriate nucleophile.…”

4,4′‐Disubstituted L‐Prolines as Highly Enantioselective Catalysts for Direct Aldol Reactions

“…[17] Double alkylation of compound 7, reduction of 8, and acid hydrolysis of 9 gave the 4,4'-disubstituted proline 1e (Scheme 2). [18] Once the catalysts had been prepared, they were tested in the classical direct aldol reaction of acetone with p-nitrobenzaldehyde as model to examine their efficiency ( Table 1). The reaction was initially per- [a] Isolated yield.…”

Design, Synthesis, Conformational Analysis and Application of Azabicyclo­alkane Amino Acids as Constrained Dipeptide Mimics

“…27 Having established the feasibility of our synthetic sequence on compounds of type V, we have extended its application to spiro compound 70 as indicated in the retrosynthetic sequence depicted in Scheme 14. 27 Attachment of a spirocyclopentane to the 4-position of methyl N-Boc pyroglutamate was achieved by a double allylation reaction of the pyroglutamate 91 42 hemiaminal which was treated with trimethylorthoformate in methanol to give the N-Boc-N,O-acetal 95 in a diastereomeric ratio >95:5. Reaction of the crude amethoxy carbamate 95 with excess allyltrimethylsilane in the presence of an equimolar amount of InCl 3 in dichloromethane at room temperature afforded the allylated adduct 96 in good yield.…”