학술논문
Versatile Access to 2Aminocyclobutene1carboxylic Acid Derivatives and Their Incorporation into Small PeptidesCyclopropyl Building Blocks for Organic Synthesis, 155. Part 154: A. de Meijere, A. F. Khlebnikov, H. W. Sünnemann, K. Rauch, D. S. Yufit, Eur. J. Org. Chem., submitted. Part 153: M. Limbach, A. V. Lygin, V. S. Korotkov, M. EsSayed, A. de Meijere, Org. Biomol. Chem.2009, 7, 3338–3342.
Document Type
Article
Source
European Journal of Organic Chemistry; July 2010, Vol. 2010 Issue: 19 p3665-3671, 7p
Subject
Language
ISSN
1434193X; 10990690
Abstract
Under a newly developed set of mild conditions [EtNiPr2, LiI, DMF, 20 °C, 3 d], methyl 2chloro2cyclopropylideneacetate 1 smoothly undergoes Michael addition ofvarious benzylamines 4 examples with ensuing ring enlargement and elimination to give in very good yields 81–99 the correspondingly substituted methyl 2benzylaminocyclobutenecarboxylates 3a–d, which were subsequently converted into the NBocprotected derivatives 4a–d. After hydrolysis of the esters, the free βamino acids 5a,bwere cleanly condensed with the methyl esters of glycine, Sproline, Sphenylglycine and Stryptophan to give the dipeptides 6a–8a, 9bin 58–89 yield. The cyclic dipeptides 15e,f, consisting of a 2aminocyclobutenecarboxylic acid and a glycine fragment, were obtained in 38 and 45 yield, respectively, upon treatment of the spirocyclopropanated chlorohexahydrodiazepinediones 10e,fwith sodium cyanide in DMSO at elevated temperatures. Palladiumcatalyzed hydrogenation of 4aafforded methyl NBoc2aminocyclobutanecarboxylate 19as a mixture of cisand transisomers.