Caveat in the stereochemical outcome of the organocatalytic Diels–Alder reaction in PEG-400
作者:Pantapalli M. Anitha、Prathama S. Mainkar、Shivakrishna Kallepu、V. S. Phani Babu、Cirandur Suresh Reddy、Srivari Chandrasekhar
DOI:10.1039/c6ra15035g
日期:——
The organocatalyticDiels–Alderreaction in non-conventional solvent (PEG-400) has yielded cycloaddition products with diastereoselectivities hitherto not reported in detail using classical reaction conditions.
Studies in Lewis acid and LiClO4 (or Nafion-H) catalysed ionic Diels-Alder reactions of chiral and achiral olefinic acetals respectively
作者:R Kumareswaran、Padma S Vankar、M Venkat Ram Reddy、Sangeeta V Pitre、Raja Roy、Yashwant D Vankar
DOI:10.1016/s0040-4020(98)01088-6
日期:1999.1
Chiral olefinic acetals derived from crotonaldehyde undergo ionicDiels-Alderreaction giving the corresponding cycloadducts in moderate to good diastereoselectivities. A variety of achiral olefinic acetals react with isoprene and cyclopentadiene to form the cycloadducts in good to excellent yields when catalysed by 4M LiClO4 in nitromethane or by Nafion-H in dichloromethane.
Three's a crowd: The combination of a Brønstedacid and a hydrogen‐bond donor cocatalyst was found to promote various ionic [2+4] cycloadditions under mild reaction conditions (see scheme; Ts=4‐toluenesulfonyl). Thiophosphoramides are the most effective cocatalysts because of the stronger counterion activation effect resulting from three, rather than two, hydrogen bonds involved in anion binding.
Indium trichloride: a useful catalyst for ionic Diels–Alder reactions
作者:B.Gopal Reddy、R Kumareswaran、Y.D Vankar
DOI:10.1016/s0040-4039(00)01857-8
日期:2000.12
Indium trichloride (20 mol%) in nitromethane permits ionic Diels-Alder reaction of a variety of 2,3-olefinic acetals to form the corresponding cycloadducts in good yields with good endo selectivities. (C) 2000 Elsevier Science Ltd. All rights reserved.
The first asymmetricchiral N-triflylphosphoramide-catalyzed ionic [2+4] cycloaddition reaction of unsaturated acetals is described. This reaction proceeds through the intermediacy of a vinyl oxocarbenium/chiral anion pair, and the chiral N-triflylphosphoramide anion controls the stereoselectivity of the cycloaddition step. Moderate enantioselectivities (up to 80:20 e.r.) have been obtained when α