L. Leite

Tautomerism and vapor-phase transformations of 2-hydroxytetrahydrofuran

The relative stability of 2-hydroxytetrahydrofuran and the tautomeric 4-hydroxybutanal was determined by the semi-empirical AM1 method. It was concluded that the cyclic tautomer predominates in the gas phase at 25°C. Vapor-phase dehydration of 2-hydroxytetrahydrofuran in the presence of porcelain and silica gel L leads to a quantitative yield of 2,3-dihydrofuran.

Synthesis and Cytotoxic Activity of 4-Substituted 3-Cyano-6,6-dimethyl-5,6-dihydro-2-pyranones

The respective 4-(arylvinyl)lactones and compounds of the Michael adduct type were synthesized by the condensation of substituted benzaldehydes with 3-cyano-4,6,6-trimethyl-5,6-dihydro-2-pyranone in the presence of catalytic amounts of sodium hydroxide. It was shown by the semiempirical AM1 method that the indicated products can be formed through one and the same intermediate compound. Some of the synthesized phenylvinyl-5,6-dihydro-2-pyranones have a cytotoxic effect, and this corresponds to the prognosis of the OREX expert system.

Synthesis and Photoisomerization of 3-Cyano-6,6-dimethyl-4-(4-nitrophenylvinyl)-5,6-dihydropyran-2-one

The condensation of 4-nitrobenzaldehyde with 3-cyano-4,6,6-trimethyl-5,6-dihydropyran-2-one leads to the formation of a crotonization product and a compound of the Michael adduct type. The main product of the photochemical conversion of (E)-3-cyano-6,6-dimethyl-4-(4-nitrophenylvinyl)-5,6-dihydropyran-2-one is the Z-isomer. Investigation of the photoisomerization of 3-cyano-6,6-dimethyl-4-(4-nitrophenylvinyl)-5,6-dihydropyran-2-one by the semiempirical AM1 method showed that in the ground state the E-isomer was thermodynamically more stable than the E-isomer. E-Z-photoisomerization is effected most probably through the lowest excited singlet state S1.

Quantum chemical investigation by the AM1 method of the catalytic cyclodehydration of 1,4-butanediol

Abstract1,4-Butanediol is converted into tetrahydrofuran in the presence of silica gel at temperatures of 245–340°C. The mechanism of the conversion of 1,4-butanediol has been studied by the quantum chemical AM1 method with full optimization of the geometry. It was established that two parallel reactions are possible depending on the conformation of the molecule. The cyclodehydration reaction is effected by conversion of a semicyclic conformer of the protonated diol molecule at a basic center of the catalyst by a concerted mechanism. The heat of the reaction forming tetrahydrofuran is —161.768 kcal/mole.

QUANTUM-CHEMICAL MODELING OF THE REACTION OF 3-PYRIDINE- CARBALDEHYDE WITH 3-CYANO- 4,5,5-TRIMETHYL-2(5H)-FURANONE

The condensation of pyridinecarbaldehydes with 3-cyano-4,5,5-trimethyl-2(5H)-furanone and 3-cyano-4,6,6-trimethyl-5,6-dihydro-2(2H)-pyranone leads to the formation of the products of crotonic condensation and compounds of the Michael adduct type. A model investigation of the mechanism by the semiempirical AM1 quantum-chemical method for the case of the reaction of 3-pyridinecarbaldehyde with 3-cyano-4,5,5-trimethyl-2(5H)-furanone showed that the products can be formed in parallel from one and the same intermediate compound.