title: A Novel Class of Conformationally Constrained, Masked Cysteines: Synthesis of 2-Alkyl- and 2-Arylsulfanyl-1-aminocyclopropanecarboxylic Acids.
abstract: A convenient synthesis of 4-sulfanylmethylene-5(4H)-oxazolones 3 was realized starting from 4-(chloromethylene)oxazolone 1 and mercaptans 2. Oxazolones 3 were used as starting materials for the preparation of unknown 2-sulfanyl-1-aminocyclopropanecarboxylic acid derivatives 5 and7. Oxazolones 3 were cyclopropanated at the exocyclic double bond with diazomethane, giving a mixture of the two (Z)- and (E)-spirocyclopropane oxazolones 4 with good diastereoselectivity. These were then treated with ethanol and DMAP to produce the corresponding carboxylates 5. The trityl derivative 5d was converted into a mixture of diastereoisomeric disulfides 6 using iodine in ethanol solution. Disulfides 6 are convenient synthons for the preparation of 3-sulfanyl-substituted 2,3-methanoamino acids 7.
authors.affiliation: Istituto di Chimica Organica, Facoltà di Farmacia, Università di Milano, Via Venezian 21, I-20133 Milano, Italy.
authors.forename: F.
authors.initials: F
authors.lastname: Clerici
authors.forename: M. L.
authors.initials: ML
authors.lastname: Gelmi
authors.forename: D.
authors.initials: D
authors.lastname: Pocar