The products of an imino Diels–Alder reaction with 2-trimethylsilyloxycyclohexadiene: synthesis, X-ray crystal structures, and mechanistic implications

Birkinshaw, Timothy N.; Tabor, Alethea B.; Holmes, Andrew B.; Kaye, Perry T.; Mayne, P. M.; Raithby, Paul R.

doi:10.1039/c39880001599

Cited by 28 publications

(8 citation statements)

References 2 publications

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“…The heteroDiels ± Alder reaction of carbonyl compounds, and probably also the aza-Diels ± Alder reaction of imino dienophiles can proceed via three possible courses: a concerted cycloaddition-, a step-wise-, and a Mannich-type process. [23,24] It has been found that the reaction paths are very much depending on both diene, dienophile and reaction conditions. [23] For a specific reaction, the reaction courses can also vary from a Diels ± Alder reaction to a Mannich-type addition reaction and solvents, temperature, and Lewis acids can have significant influence on the reaction courses.…”

Section: Mechanistic Aspectsmentioning

confidence: 99%

“…[23] For a specific reaction, the reaction courses can also vary from a Diels ± Alder reaction to a Mannich-type addition reaction and solvents, temperature, and Lewis acids can have significant influence on the reaction courses. [24] For the present catalytic enantioselective reactions, both the aza-Diels ± Alder and Mannich-type addition (or ene) products were formed depending on the dienes and imines used. For the reaction of the N-tosyl a-imino ester 1 a with activated acyclic dienes such as Danishefskys diene 2 a and the dimethyl-substituted Danishefskys diene 2 b, only the aza-Diels ± Alder products 3 a and 3 b are isolated in high yields under the standard reaction conditions for the activated dienes (BINAP-or phosphino ± oxazoline CuClO 4 -catalysts (10 mol %) at À 78 8C in various solvents such as CH 2 Cl 2 , THF, Et 2 O, tert-butyl methyl ether, toluene, and MeCN for 15 ± 20 h followed by a TFA quench (2 % TFA in CH 2 Cl 2 )).…”

Section: Mechanistic Aspectsmentioning

confidence: 99%

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Catalytic Enantioselective Aza-Diels-Alder Reactions of Imines-An Approach to Optically Active Nonproteinogenicα-Amino Acids

et al. 2000

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A catalytic enantioselective aza-Diels-Alder reaction of imines has been developed. The reaction of N-tosyl alpha-imino ester with different dienes including activated, non-activated, cyclic, and acyclic dienes has been investigated in the presence of various chiral Lewis acids. A series of phosphino-oxazoline ligands have been synthesized and evaluated for the reaction. It was found that the combination of phosphino-oxazoline ligands with copper(I) salts gives the best results for the activated dienes, while BINAP-copper(I) complexes are good catalysts for all the dienes studied. In the case of activated acyclic dienes the aza-Diels-Alder products can be obtained in higher than 80% isolated yield and 96% ee, while for the unactivated cyclic dienes the exo diastereomer is formed as the major product in up to 95 % ee. For an activated cyclic conjugated diene, 2-trimethylsilyloxy-1,3-cyclohexadiene, the reaction proceeds as a Mannich-type addition reaction giving optically active gamma-oxo alpha-amino acid derivatives in good yields and up to 96% ee. The reaction of an unactivated acyclic diene, 2,3-dimethyl-1,3-butadiene, with the N-tosyl alpha-imino ester gives both the aza-Diels-Alder and aza-ene products, in a ratio of 9:1 favoring the aza-Diels-Alder product. Furthermore, a series of different imines have been synthesized and investigated as possible substrates for the present catalytic enantioselective aza-Diels-Alder reaction in order to obtain mechanistic insight. All imines studied gave moderate to high ee. Particularly, the reaction of the N-phenyl and N-p-methoxyphenyl substituted glyoxylate imines with Danishefsky's diene proceeded well affording the corresponding aza-Diels-Alder product in high yield with up to 91% ee at room temperature. The present catalytic enantioselective reaction of imines provided an effective route to optically active nonproteinogenic alpha-amino acids. The products of the catalytic enantioselective aza-Diels-Alder reaction of the cyclic dienes can be used for the preparation of key compounds such as natural products and compounds of pharmaceutical interest. The absolute configurations of five products have been solved by X-ray structural analysis, and it is found that the absolute configuration of the aza-Diels-Alder adduct is dependent on the substituent on the imine nitrogen atom. It turned out that the N-tosyl glyoxylate imine and N-p-methoxyphenyl glyoxylate imine give the aza-Diels-Alder adduct with opposite absolute configuration using the same enantiomer of the catalyst. On the basis of the results the mechanistic aspects for the reactions are discussed.

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Section: Mechanistic Aspectsmentioning

confidence: 99%

Section: Mechanistic Aspectsmentioning

confidence: 99%

Catalytic Enantioselective Aza-Diels-Alder Reactions of Imines-An Approach to Optically Active Nonproteinogenicα-Amino Acids

et al. 2000

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“…11; examples of such a stepwise addition-cyclization mechanism have been reported earlier for the reaction of silylenol ethers with aldimines (Birkinshaw et al 1988;Kobayashi et al 1995;Hermitage et al 2004)]. In the first step, analogous to our previous reported ion pair catalysis (Rueping et al 2005a(Rueping et al ,b, 2006a(Rueping et al -e, 2007a), a proton transfer from the chiral Brønsted acid 5 to the aldimine occurs and the chiral ion pair A is formed which is now activated to react with the nucleophile.…”

Section: Synthesis Of Isoquinuclidinesmentioning

confidence: 66%

New Developments in Enantioselective Brønsted Acid Catalysis: Chiral Ion Pair Catalysis and Beyond

Rueping¹,

Sugiono²

2008

Ernst Schering Foundation Symposium Proceedings

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“…The isoquinuclidine unit serves as a precursor for the synthesis of naturally occurring piperidine alkaloids of the prosopis family (Birkinshaw et al, 1988). The structure of the title compound, (I), is reported here as part of our ongoing structural study of this series of compounds (Ravikumar et al, 2005(Ravikumar et al, , 2006.…”

Section: Commentmentioning

confidence: 99%

(3Z)-2-Benzyl-3-benzylidene-6-phenyl-2-azabicyclo[2.2.2]octan-5-one

et al. 2007

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The products of an imino Diels–Alder reaction with 2-trimethylsilyloxycyclohexadiene: synthesis, X-ray crystal structures, and mechanistic implications

Cited by 28 publications

References 2 publications

Catalytic Enantioselective Aza-Diels-Alder Reactions of Imines-An Approach to Optically Active Nonproteinogenicα-Amino Acids

Catalytic Enantioselective Aza-Diels-Alder Reactions of Imines-An Approach to Optically Active Nonproteinogenicα-Amino Acids

New Developments in Enantioselective Brønsted Acid Catalysis: Chiral Ion Pair Catalysis and Beyond

(3Z)-2-Benzyl-3-benzylidene-6-phenyl-2-azabicyclo[2.2.2]octan-5-one

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