A New and Efficient Access to Thiazoline-4-carboxylates and Cysteine Derivatives Incorporating Cyclopropyl Groups
摘要:
Under basic conditions (NaHCO3, MeCN), thiocarboxamides 2, including NN-thioureas, cleanly undergo Michael addition onto 2-chloro-2-cyclopropylideneacetates 1, attacking through the sulfur, and this is followed by an intramolecular substitution to afford 5-spirocyclopropane-annelated thiazoline-4-carboxylates 4 in 37-92% yields. The thiazolines 4 are cysteine derivatives that possess a cyclopropyl or substituted cyclopropyl group in place of the gem-dimethyl-substituted beta -carbon atom of penicillamine; they can be hydrolyzed to the hydrochloride salt of the amino acid 5 by heating in acid. Under acidic conditions (CH2Cl2, HCl), the Michael adducts 7 of thioamides 2 onto 1 are formed in high to virtually quantitative yields. When treated with NaHCO3 in MeCN, the adducts 7 cyclize to thiazolinecarboxylates 4 (51-82%), but in the presence of Ti(OiPr)(4) they form spirocyclopropane-annelated thiazinones 8 (19-88%).
Cyclopropyl building blocks for organic synthesis. Part 22. Facile synthesis of stable analogs of 2-oxocyclobutanecarboxylates: 2-[(diphenylmethylene)amino]cyclobutenecarboxylates, derivatives and reactions
作者:Ludger Wessjohann、Karsten Giller、Bernd Zuck、Lars Skatteboel、Armin de Meijere
DOI:10.1021/jo00075a047
日期:1993.11
An efficient two-step synthesis of 2-[(diphenylmethylene)amino]cyclobutenecarboxylate (4a) and some analogous derivatives from 2-chloro-2-cyclopropylideneacetates 2, 17, 22, and 25 and nonenolizable ketimines, especially diphenylmethyleneamine (DPMA-H), is described. A likely mechanism for the formation of 4a from the primary Michael adduct 3 of DPMA-H to 2 and its substituted analogues is presented. The unique neighboring group effect of the DPMA moiety to allow formation of an azaspiropentane intermediate and its regioselective rearrangement to cyclobutenamine derivatives is discussed and further exemplified by an extremely facile SET alpha-chlorination. Compound 4a and derivatives undergo a thermal ring-opening reaction to the corresponding butadienes with subsequent formation of 1,3-disubstituted 3,4-dihydroisoquinolines 39. Further transformations of 4a and some derivatives include transesterification, hydrolysis to methyl 2-oxocyclobutanecarboxylates, and addition of N-phenyltriazolinedione.