Hindered Ureas as Masked Isocyanates: Facile Carbamoylation of Nucleophiles under Neutral Conditions
作者:Marc Hutchby、Chris E. Houlden、J. Gair Ford、Simon N. G. Tyler、Michel R. Gagné、Guy C. Lloyd-Jones、Kevin I. Booker-Milburn
DOI:10.1002/anie.200904435
日期:2009.11.2
better: Sterically hindered dialkyl ureas undergo nucleophilic substitution at dramatically faster rates than their less hindered counterparts (see scheme). Steric decompression upon the formation of an intermediate isocyanate can explain this counterintuitive behavior. These hindered ureas can be considered as masked reagents that liberate reactive isocyanates in situ.
越大越好:空间受阻的二烷基脲以比受阻较小的对应物快得多的速率进行亲核取代(参见方案)。中间体异氰酸酯形成时的空间减压可以解释这种违反直觉的行为。这些受阻尿素可以被认为是原位释放反应性异氰酸酯的掩蔽试剂。