über die [3+2]-Cycloaddition von Nitronen 和 Isothiocyanate
摘要:
Die Nitrone 1 cyclisieren im allgemeinen mit Isothiocyanaten 2 zu 1,2,4-Oxadiazolidin-5-thionen 3, in seltenen Fällen jedoch zu 1,2,4-Oxadiazolidin-5-onen 4. Dinitrone des Glyso ) die Produkte 9 bzw。10.
作者:Jonathan T. Reeves、Chris Lorenc、Kaddy Camara、Zhibin Li、Heewon Lee、Carl A. Busacca、Chris H. Senanayake
DOI:10.1021/jo500848a
日期:2014.6.20
The addition of carbamoyl anions derivedfrom N,N-disubstituted formamides and LDA to N-tert-butyl nitrones is described. The reaction was demonstrated with a variety of formamides and nitrones and provided a direct route to α-(N-hydroxy)amino amides. The use of a tert-leucinol derivedchiralauxiliary on the nitrone provided products in good diastereoselectivity. Derivatization of the products by
Steric effects on regioselectivity in 1.3-Dipolar cycloaddition of C,N-dialyl nitrones with acceptor-substituted alkynes
作者:Hans Günter Aurich、Michael Franzke、Hans Peter Kesselheim、Markus Rohr
DOI:10.1016/s0040-4020(01)88127-8
日期:——
The 1.3 dipolar cycloaddition of alkynes 4-6 with acyclic nitrones 1-3, 23 and 24 as well as with cyclic nitrones 27 is studied. As was found for the reaction of the aldonitrones 1-3 an increased portion of 5-regioisomers is formed with increasing steric demand of either of the two substituents, the C-alkyl substituent R2 and the N-alkyl substituent R1. Thus the conclusion is drawn that cycloaddition of 1-3 proceeds not only via transition states arising from Z-nitrones but also via transition states developing from E-nitrones, although in the ground-state the Z-isomer is favored to a considerable extent. In this context steric destabilization of the transition states is discussed qualitatively.