CHAPTER 5: Serebryakov-Jørgensen Dienamines (1-Aminobuta-1,3-Dienes): Different in situ Generation Methods and Applications in [4+2]-Cycloadditions

Abstract

As well as α,β-unsaturated aldehydes, linear deconjugated enones or allylic ketones have reacted, in a few cases, with amine catalysts to generate the reactive 1-aminobuta-1,3-dienes (Serebryakov-Jørgensen dienamines) in situ. These dienamines are involved in [4+2]-cycloadditions as the electron-rich diene source with a variety of electron-deficient dienophiles, such as isatins, 1,4-benzo- and 1,4-naphtho-quinones, coumarin-3-carboxylic acids, sulfonyl Nazarov reagents, nitroolefins, etc. These also reacted as electron-rich dienophiles with diverse electron-deficient dienes, like N-tosyl-1-azabuta-1,3-diene systems, chromone-fused dienes, unsaturated α-ketoesters, α,β-unsaturated acyl phosphonates, α-bromo-(trifluoromethyl)-enones, alkylidene pyrazolones and α-cyano-α,β-unsaturated ketones. Exploitation of these dienamines resulted in the asymmetric synthesis of a library of significant scaffolds, methyl 1,3-cyclohexadienecarboxylates, trisubstituted cyclohexadienes, spirocyclic oxindoles, dihydrodibenzofurans, steroids, bridged tricyclic benzopyrans, trans,trans-6-nitrocyclohex-2-enyl amines and cis,trans-nitrocyclohexenyl amides, methylene bridged benzo[1,5]oxazocines, piperidine derivatives, decahydroisoquinolines, caged tetrahydroxanthones, dihydropyran derivatives, dihydropyran phosphonates and highly substituted CF3-dihydropyrans, and tetrahydropyranopyrazoles by several groups, proving their resourcefulness. Self-dimerization of (E)-4-acetoxycrotonaldehyde elegantly furnished a Diels-Alder adduct, which was utilized in the total synthesis of (+)-palitantines. Dynamic kinetic resolution of racemic 5-acyloxydihydropyranones and 2-cyclohexylidene acetaldehydes was achieved efficiently through Serebryakov-Jørgensen dienamines resulting in the synthesis of substituted tetrahydro-1H-isochromanes and tricyclic chromane-2-one derivatives, respectively. Desymmetrization of substituted cyclohexadienones was accomplished, producing the highly asymmetric synthesis of tricyclic derivatives.