110318-19-9Relevant academic research and scientific papers
Multistep Inverse Diels-Alder Reactions of 1,3-Dimethyl-2-methyleneimidazolidine with Methyl 2,4-Hexadienoates
Heuschmann, Manfred
, p. 39 - 50 (2007/10/02)
2-Methyleneimidazolidine 1 and hexadienoates 2 form diastereomeric cycloadducts 3a and b, which slowly rearrange to give 4 and 5, and Michaelic adducts 6, 7, and 9.Evaluation of the kinetics by means of 1H- and 13C-NMR spectroscopy and computer assisted simulation shows that the cycloadducts 3 and the Michael adduct 6 are formed via a common intermediate.The difference in stereoselectivity in the reactions of the diastereomeric hexadienoates 2a,b and c corroborates the multi-step mechanism of the cycloaddition.Deuterium labelling of 1 proofs interrelations between the loss of stereospecivity and the equilibrium of the starting materials 1 and 2 with 6.Chiral dienophiles like 15 react stereospecifically with 2a and b.The nature of the intermediate and the mechanism of its rearrangement to the cycloadducts are discussed in terms of energetics and stereochemistry.
2-Alkylidenimidazolidines - Ketene Equivalents in the Inverse Diels-Alder Reaction
Gruseck, Ursula,Heuschmann, Manfred
, p. 2065 - 2074 (2007/10/02)
2-Alkylideneimidazolidines 1 and 2,4-dienoates 2 form cycloadducts at or below room temperature, which are mildly hydrolysed by dilute acid to form derivatives of 2-cyclohexenone and 1,3-cyclohexadienol.The structures of the cis/trans-disubstituted cyclohexenones 14 and 15 were determined by means of 13C-NMR spectroscopy.The cis/trans ratio can be influenced through the choice of the 2-alkylideneimidazolidines 1.Especially N-phenylsubstituted derivatives form trans products 15 stereoselectively but not stereospecifically.The reason for this selectivity is discussed with regard to the multi-step mechanism of the cycloaddition.Depending on the structure of the starting materials 1 and 2, michael additions and acid-base reactions are observed besides cycloadditions.
