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The preparation of 2-phenyl-4-dimethylamino-1-aza-, 1-oxa-, 1-thia-, 1-selena-3-azabuta-1,3-dienes as well as their 4-methyl derivatives is described following a new heteroatom interchange reaction process. Heteronucleophilic attack at one particular reactive site of bis-electrophilic amidinium salts is the key feature of the process. In addition, we also disclose that the substituted 1-oxa-3-aza- and 1,3-diazabuta-1,3-dienes can be obtained by a reactional transformation cascade initiated by either silver acetate addition or tosyl azide [3+2] cycloaddition onto the CS or CSe double bonds of the 1-thia- and 1-selena-3-azabuta-1,3-diene analogues.

New 2-aza-1,3-dienes bearing 1 and 3-donor substituents are prepared from N-thioacylacetamidines through deprotonation of N-ylidene acetamidinium iodides. The 2-aza-3-(dimethylamino)-1-(methylthio)-1-phenylbutadiene (3) is trapped in situ by the residual precursor salt acting as a heterodienophile to give the pyrimidine 5. Substituted 2-aza-1-(dimethylamino)-3-(methylthio) analogues react readily with a variety of electron-deficient dienophiles to yield pyridine or pyrimidine derivatives. The stereochemistry of the hetero Diels-Alder reaction in the cases of dimethyl fumarate and acrylonitrile has been assigned by X-ray diffraction analyses of the resulting tetrahydropyridines and corresponds to an exo selectivity. The number and nature of cycloadducts in the cases of dimethyl acetylenedicarboxylate and phenyl isothiocyanate depend on C-4 substitution. The results obtained from the C-4 unsubstituted azabutadiene 8 are explained by an allylic rearrangement involving the 1,3-migration of dimethylamino group in the primary [4+2] adduct.

New 2-aza-1,3-dienes bearing 1 and 3-donor substituents are prepared from N-thioacylacetamidines through deprotonation of N-ylidene acetamidinium iodides. The 2-aza-3-(dimethylamino)-1-(methylthio)-1-phenylbutadiene (3) is trapped in situ by the residual precursor salt acting as a heterodienophile to give the pyrimidine 5. Substituted 2-aza-1-(dimethylamino)-3-(methylthio) analogues react readily with a variety of electron-deficient dienophiles to yield pyridine or pyrimidine derivatives. The stereochemistry of the hetero Diels-Alder reaction in the cases of dimethyl fumarate and acrylonitrile has been assigned by X-ray diffraction analyses of the resulting tetrahydropyridines and corresponds to an exo selectivity. The number and nature of cycloadducts in the cases of dimethyl acetylenedicarboxylate and phenyl isothiocyanate depend on C-4 substitution. The results obtained from the C-4 unsubstituted azabutadiene 8 are explained by an allylic rearrangement involving the 1,3-migration of dimethylamino group in the primary [4+2] adduct.

The preparation of 2-phenyl-4-dimethylamino-1-aza-, 1-oxa-, 1-thia-, 1-selena-3-azabuta-1,3-dienes as well as their 4-methyl derivatives is described following a new heteroatom interchange reaction process. Heteronucleophilic attack at one particular reactive site of bis-electrophilic amidinium salts is the key feature of the process. In addition, we also disclose that the substituted 1-oxa-3-aza- and 1,3-diazabuta-1,3-dienes can be obtained by a reactional transformation cascade initiated by either silver acetate addition or tosyl azide [3+2] cycloaddition onto the CS or CSe double bonds of the 1-thia- and 1-selena-3-azabuta-1,3-diene analogues.

Electrochemical and chemical reductions are complementary methods for the selective hydrogenation of 2-substituted-6-methoxycarbonyl-4H-1,3-thiazine-4-ones leading to 2,3-dihydro; 5,6-dihydro- and 2,3,5,6-tetrahydro-4H-1,3-thiazine-4-ones without ring opening and ketone function alteration. Selective hydrogenation of the imine bond (C[dbnd]N) or the alkene bond (C[dbnd]C) depends on the nature of the heteroatomic substituent [(CH3)2N, C2H2O, C6H5CH2S] at the 2 position. La reduction par voie electrochimique (a potentiel controˇle et sur cathode de mercure) et par voie chimique (borohydrures, hydrure de tributyletain, hydrure de triethylsilane, aluminium amalgame) des 6-methoxycarbonyl-4H-1,3-thiazine-4-ones substituees en position 2 par un groupement aromatique ou heteroatomique permet l'obtention selective des 2,3-dihydro; 5,6-dihydro- et 2,3,5,6-tetrahydro-4H-1,3-thiazine-4-ones correspondantes, sans ouverture du cycle thiazinique ni alteration de la fontion cetonique. L'orientation de la reduc...

The thioamide vinylogues (2-aminovinyl thioketones) react as heterodienes with open-chain and cyclic dienophiles to give substituted 4-amino-3,4-dihydro-2H-thiopyrans, or substituted 2H-thiopyrans and substituted 7 - methyl - 7,7a - dihydro - 5H - thiopyranno[2,3 - c] - 5 - furanones respectively, in good agreement with calculated perturbation energy of second order.

2-Phenyl-4-dimethylamino-1-thia-3-azabutadiene and methylacrylate gave 5,6-dihydro-4H-1,3-thiazine by 4 + 2 cyclocondensation reaction at 55°C. The heterodienes configuration was established by X-Ray spectra. The Diels-Alder character of this reversible reaction was indicated by kinetic and thermodynamic parameters determined by 1H N.M.R.

(4+2)cyclocondensation reactions under high pressure between methylacrylate and 2-substitutes 1-thia 3-aza 4-aminobutadienes leads selectively to 2-substituted 5-methoxycarbonyl 6H-1,3-thiazines.