Evidence for the non-concerted 4+2 -cycloaddition of N-aryl imines when acting as both dienophiles and dienes under Lewis acid-catalysed conditions

The ytterbium(III) triflate-catalysed reaction of a para-methoxyaniline, ethyl glyoxalate-derived imine, with a series of different dienes has resulted in products which initially suggest the operation of two possible modes of aza-Diels-Alder reaction, however, a more likely explanation is that a common reaction mechanism is operating, involving a stepwise Lewis acid-catalysed process and a common type of zwitterionic ytterbium complex. (C) 2002 Elsevier Science Ltd. All rights reserved

p-Tolylsulfonyl cyanide

The first crystal structure of a sulfonyl cyanide, C8H7NO2S, has been determined. The molecule has an unusual bond-length distribution, with a very long S-Csp bond [1.772 (2) Angstrom] and a short S-Csp(2) bond [1.7368 (17) Angstrom]

Absolute Stereochemistry Assignment of N-Phosphorylimine-Derived Aza-Diels-Alder Adducts with TDDFT CD Calculations

N-Phosphorylimines undergo Lewis acid-catalyzed Diels-Alder reactions with Danishefsky’s diene. Application of the chiral catalyst zinc(II)-(S)-BINOL results in good-to-low asymmetric induction but poor chemical conversion. However, the absolute stereochemistry of novel aza-Diels-Alder cycloadducts, such as diethyl 4-oxo-2-phenyl-3,4-dihydropyridin-1(2H)-ylphosphonate, can be determined using circular dichroism (CD). Comparison between experimental and TDDFT-calculated CD spectrum shows that use of the (S)-catalyst results in predominant formation of the (6R) cycloadducts

Absolute stereochemistry assignment of N-phosphorylimine-derived aza-Diels-Alder adducts with TDDFF CD calculations

N-Phosphorylimines undergo Lewis acid-catalyzed Diels-Alder reactions with Danishefsky's diene. Application of the chiral catalyst zinc (II)- (S)-BINOL results in good-to-low asymmetric induction but poor chemical conversion. However, the absolute stereochemistry of novel aza-Diels-Alder cycloadducts, such as diethyl 4-oxo-2-phenyl-3,4-dihydropyridin-1(2H)-ylphosphonate, can be determined using circular dichroism (CD). Comparison between experimental and TDDFT-calculated CD spectrum shows that use of the (S)-catalyst results in predominant formation of the (6R) cycloadducts. (c) 2005 Wiley-Liss, Inc

Mechanistic studies on the formal aza-Diels-Alder reactions of N-aryl imines: evidence for the non-concertedness under Lewis-acid catalysed conditions

The reaction of a para-methoxyaniline, ethyl glyoxalate-derived imine with a series of dienes has resulted in products, which initially suggest the operation of different modes of aza-Diels-Alder reaction. However, a more likely explanation is that a common reaction mechanism is operating, involving a step-wise Lewis-acid catalysed process, which only appears to behave similarly to alternative concerted cycloaddition reactions

Lewis Acid-catalysed Aza-Diels–Alder versus Mannich Reactions of N-Diethyl Phosphoryl Imino Dienophiles with Oxygenated Dienes and Application of a Chiral Lewis Acid

N-Phosphoryl imines react with oxygenated dienes in the presence of Lewis acids to provide either the formal aza-Diels-Alder adduct, or the acyclic Mannich-type addition product, depending upon the catalyst and work up used, which is in agreement with the hypothesis that these reactions are mediated by zwitterionic Lewis acid-complex intermediates, rather than a concerted cyclo-addition transition-state followed by hydrolytic ring opening. Stoichiometric asymmetric induction can be achieved using a zinc(II)binol complex, producing up 77% ee

Lewis acid-catalysed aza-Diels-Alder versus Mannich reactions of N-diethyl phosphoryl imino dienophiles with oxygenated dienes and application of a chiral lewis acid

N-Phosphoryl imines react with oxygenated dienes in the presence of Lewis acids to provide either the formal aza-Diels-Alder adduct, or the acyclic Mannich-type addition product, depending upon the catalyst and work up used, which is in agreement with the hypothesis that these reactions are mediated by zwitterionic Lewis acid-complex intermediates, rather than a concerted cyclo-addition transition-state followed by hydrolytic ring opening. Stoichiometric asymmetric induction can be achieved using a zinc(II)binol complex, producing up 77% ee

Lewis acid-catalysed aza-Diels-Alder versus Mannich reactions of N-diethyl phosphoryl imino dienophiles with oxygenated dienes and application of a chiral lewis acid

N-Phosphoryl imines react with oxygenated dienes in the presence of Lewis acids to provide either the formal aza-Diels-Alder adduct, or the acyclic Mannich-type addition product, depending upon the catalyst and work up used, which is in agreement with the hypothesis that these reactions are mediated by zwitterionic Lewis acid-complex intermediates, rather than a concerted cyclo-addition transition-state followed by hydrolytic ring opening. Stoichiometric asymmetric induction can be achieved using a zinc(II)binol complex, producing up 77% ee