Microwave-assisted tandem Wittig–intramolecular Diels–Alder cycloaddition. Product distribution and stereochemical assignment
摘要:
The IMDA cycloadditions of 10 different ester-tethered 1,3,8-nonatrienes have been examined under controlled microwave heating (MeCN, 180 degrees C, 30 min), giving 90-99% yields, and the stereochemical outcome of the exo and endo adducts established together with X-ray crystal structural analysis. A microwave-assisted tandem Wittig-IMDA cycloaddition protocol has been established for a modular synthesis of the bicyclic lactones starting from alpha-bromoacetates of 2,4-pentadien-1-ols and alpha-oxo carbonyl compounds in the presence of PPh3 and 2,6-lutidine (MeCN, 180 degrees C, 30 min). The overall yields of the tandem reactions are 68-80% and the stereoselectivity of the major adducts formed from E-substituted 1,3,8-nonatriene is the same as that observed for the purified 1,3,8-nonatrienes. (c) 2006 Elsevier Ltd. All rights reserved.
New insights into the endo–exo stereoselectivity of the intramolecular Diels-Alder reaction of 1,3,8-nonatrienes
作者:Michael J. Lilly、Michael N. Paddon-Row、Michael S. Sherburn、Craig I. Turner
DOI:10.1039/b006483l
日期:——
B3LYP/6-31G(d) theory predicts the experimental endo–exo selectivity of intramolecular Diels-Alderreactions of C9-substituted 1,3,8-nonatrienes: the reactions are concerted but the transition structures are remarkably asynchronous.
Intramolecular Diels−Alder Reactions of Ester-Linked 1,3,8-Nonatrienes
作者:Tory N. Cayzer、Michael N. Paddon-Row、Damian Moran、Alan D. Payne、Michael S. Sherburn、Peter Turner
DOI:10.1021/jo0505829
日期:2005.7.1
Penta-1,3-dienyl acrylates undergo kinetically controlled intramolecular Diels-Alder (lMDA) reactions and DFT calculations (B3LYP/6-31+G(d)) predict stereoselectivities that are in very good agreement with the experimental values. The nature of the diene Cl substituent has virtually no influence upon reactivity or trans/cis-stereoselectivity whereas terminal C9 dienophile substituents have a substantial effect on both the reactivity and stereoselectivity of these IMDA reactions. The TSs highlight contributions from strain in the developing tether-containing ring, and steric and electronic effects between tether and dienophile substituents, thus providing insight into the origins of IMDA reactivity and stereoselectivity.