Silica and alumina modified by Lewis acids as catalysts in Diels-Alder reactions of carbonyl-containing dienophiles
作者:Carlos Cativiela、José M. Fraile、José I. García、José A. Mayoral、Elisabet Pires、Ana J. Royo、François Figueras、Louis C. de Ménorval
DOI:10.1016/s0040-4020(01)89919-1
日期:1993.5
contain strong Lewis acids sites and are efficient catalysts in Diels-Alderreactions of carbonyl-containing dienophiles. In cyclopentadiene reactions, high conversions and endo/exo selectivities are obtained in short reaction times, without excess of diene and with a small amount of catalyst at room temperature. With less reactive dienes, temperature, diene proportion and reaction times must be increased
Inductivity and Bridging in 2-Bicyclo[2.2.2]octyl Cations. Polar Effects, Part 11
作者:Cyril A. Grob、Pawel Sawlewicz
DOI:10.1002/hlca.19840670729
日期:1984.11.7
(ρI = 0.78), probably, because in the former case bridging of C(6) is less hindered by the departing anion. The relative yields of exo- and endo-substitution products from the series 12 and 13, are in accord with graded bridging of C(6) in the incipient bicyclooctyl cations. But almost constant bridging of C(2) by C(7) is indicated in the ionization of the 2-endo-bicyclooctane series 13. Consequently
溶剂分解速率和若干6-取代的2-产品外切-和2-内型-双环[2.2.2]辛基p -toluenesulfonates,12和13分别被报道。电感,如由反应常数ρ测量余,是在相当少的外切-系列12(ρ我= -1.50)中比在相应的2-外型-norbornyl p -toluenesulfonates 1(ρ我= -2.0)。建议,出于几何原因,在双环辛烷系列12中,阳离子中心C(2)与C(6)的桥接不那么强。就像降冰片系列一样1。在另一方面,电感是在2-更高内二环辛烷系列13(ρ我= -1.0)中比在相应的2-内型-norbornane系列3(ρ我= 0.78),可能是,因为在前者的情况下桥接C(6)的原子被离去阴离子的阻碍较小。从系列12和13的exo-和内取代产物的相对产量与C(6)在初始双环辛基阳离子中的分级桥连相一致。但是在2-内膜的电离中表明了C(7)与C(2)几乎恒定的桥接-双环
Bicyclo[2.2.2]octane-2,5-carbolactone
作者:DJ Brecknell、RM Carman、PJ Day
DOI:10.1071/ch9842323
日期:——
The title compound has been
synthesized and compared with bicyclo[2.2.2]octane-2,6-carbolactone.
Ambiguities in the literature concerning the preparation of the title compound
have been resolved.
Trimethylsilyl bis(trifluoromethanesulfonyl)imide as a tolerant and environmentally benign Lewis acid catalyst of the Diels–Alder reaction
作者:Benoit Mathieu、Léon Ghosez
DOI:10.1016/s0040-4020(02)00971-7
日期:2002.10
N-trimethylsilyl bis(trifluoromethanesulfonyl)imide (TMSNTf2) was readily prepared in situ by protodesilylation of trimethylsilane, allyl- or phenyltrimethylsilane with bis(trifluoromethylsulfonyl)imide. NMR studies showed that TMSNTf2 was much more effective than TMSOTf in complexing the carbonyl group of trans-methylcrotonate. As a result, TMSNTf2 was found to be superior to TMSOTf as a catalyst for the Diels-Alder reaction of alpha,beta-unsaturated esters with a wide variety of dienes. In contrast to many metal derived Lewis acids, TMSNTf2 was found tolerant of many sensitive functional groups present in the diene partner. (C) 2002 Elsevier Science Ltd. All rights reserved.
Sopow, Zhurnal Obshchei Khimii, 1955, vol. 25, p. 2082,2087; engl. Ausg. S. 2035, 2040