A study of sensitized photooxygenation of 3,4-dihydro-2H-pyran

The photooxygenation of 3,4-dihydro-2H-pyran sensitized by cyanoanthracenes (9,10-dicyanoanthracene and 9-cyanoanthracene) in different solvents (CH₃CN, CH₃Cl_2,C₆H₆ and CCl₄) has been studied in this paper. The products, product distribution as well as solvent isotope effect are the same as those in the reaction of singlet oxygen. Fluorescence quenching, exciplex formation and free energy change also reveal that electron transfer occurs between sensitizer-excited singlet state and substrate and then singlet oxygen is formed subsequently as the reactive intermediate in the process.     

The unimolecular dissociation of 3,4-dihydro-2H-pyran over a wide temperature range

The thermal decomposition of 3,4-dihydro-2H-pyran (DHP, C₅H₈O) has been investigated by two methods: in shock waves with the laser-schlieren technique using mixtures of 5 and 10% DHP in krypton over 900–1500 K, 110–560 torr; in a flow tube having a reaction pressure 0.5 torr above atmospheric using the decomposition of allylethyl ether as an internal standard, and covering 663–773 K. The retro-Diels-Alder dissociation to the stable acrolein and ethylene is the dominant channel for all conditions. Precise rate constants (rms deviation of 10%) were obtained for this process over the indicated temperature ranges. Unimolecular falloff is evident in the shock-tube results, and RRKM calculations also predict a slight falloff at the lower temperatures. These RRKM calculations use a routine vibration model transition state and agree closely with the high-temperature data when 〈ΔE〉_down is a fixed 400 cm^?1. Arrhenius expressions for k_∞ derived from the two measurements are in close accord and also consistent with most previous studies of this reaction. © 1995 John Wiley & Sons, Inc.     

Specific features of the reaction of 3,4-dihydro-2H-pyran with 2-(chlorosulfanyl)pyridine 1-oxide

Russian Chemical Bulletin -     

2-Methyl-5,6-dihydro-2H-pyran in the simmons-smith reaction

2-Methyl-5,6-dihydro-2H-pyran reacts with the Simmons-Smith reagent to give a mixture of 2-ethyl-5,6-dihydro-2H-pyran, cis- and trans-2-methyl-3-oxabicyclo-[4.1.0]heptanes, and 2-methyl-2,5,6,7- or 3-methyl-2,3,6,7-tetrahydrooxepine in a ratio of 2251.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 449–450, April, 1987.     

Reaction of 2-methyl-5,6-dihydro-2H-pyran with dichlorocarbene

Upon treatment of 2-methyl-5,6-dihydro-2H-pyran with dichlorocarbene there are formed products of addition to the double bond and insertion at the C-H bond giving cis- and trans-7,7-dichloro-2-methyl-3-oxabicyclo[4.1.0]heptane and 2-dichloromethyl-2-methyl-5,6-dihydro-2H-pyran.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 190–191, February, 1986.     

The thermal decomposition of 4-methyl-3,6-dihydro-2H-pyran

The thermal decomposition of the title compound has been studied in the gas phase in the temperature range of 584–634 K. The decomposition was found to be a first-order homogeneous process yielding 2-methylbuta-1,3-diene and formaldehyde. The rate constants obtained at 11 temperatures within the quoted range fitted the Arrhenius equation The decomposition is probably unimolecular and concerted.     

On the synthesis of 3,4-dihydro-2H-1,2-benzothiazine 1,1-dioxides

The 3,4-dihydro-2H-1,2-benzothiazine 1,1-dioxides were prepared by reduction of the corresponding 1,2-benzothiazin-2-ones with diborane. The latter were obtained by the action of primary amines on 4,5-dimethoxy-2-carbomethoxymethylbenzenesulfonyl chloride followed by basic hydrolysis and cyclization of the formed 4,5-dimethoxy-2-carbomethoxymethylbenezenesulfonamides.     

The reaction of benzotriazoles with 3,4-dihydro-4H-pyrane and 2-acetoxymethyl-3,4-dihydro-2H-pyrane

From the reaction of benzotriazoles with 2,3-dihydro-4H-pyrane and 2-acetoxymethyl-3,4-dihydro-2H-pyrane the corresponding 1-(2-tetrahydropyranyl)benzotriazole and cis-and trans-1-(6-acetoxymethyl-2-tetrahydropyranyl)benzotriazole derivatives were obtained. The structures and conformations of these compounds were confirmed by UV and NMR spectra.     

The proton magnetic resonance spectrum of 4-t-butyl-5, 6-dihydro-4H-pyran

The proton magnetic resonance spectrum of 4-t-butyl-5,6-dihydro-4H-pyran has been analyzed with the aid of the paramagnetic shift reagent Eu(fod)₃. All hydrogen-hydrogen spin-spin coupling constants are reported and a conformation is suggested which is consistent with these data.     

The preparation of 3,4-dihydro-1-benzoxepin-5(2H)-ones

Several methods for the preparation of 3,4-dihydro-1-benzoxepin-5(2H)-ones are described. In addition to the desired ketones, a variety of novel by-products have been isolated.     

Preparation of some 3,4-dihydro-5H-1,3,5-benzotriazepines

Department of Organic Chemistry, Slovak Technical University, 812 37 Bratislava, Slovak Republic. Published in Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1383–1384, October, 1995. Original article submitted August 24, 1995.     

Synthesis of 3-benzoyl-3,4-dihydro-2H- and 3,4-dihydro-2,2-disubstituted-benzopyrans via alkynyl grignard reagents

The versatility of the new route to a substituted chromane via a lithiated allene recently described by us [1] is reported. The relatively more stable alkynols 2–4 were readily identified and thus provide evidence for the formation of vinyl acetylene carbinol as an intermediate in the new route. Accordingly, phenylacetylene magnesium bromide [2] reacted with suitable aldehyde or ketone to give the alkynols 2–4 which condensed further with the same or different aldehyde or ketone to give 3-benzoyl heteroring-substituted chromanes 5–17.     

Synthesis of 3,4-dihydro-2H-1,3,5-thiadiazines

3,4-Dihydro-2H-1,3,5-thiadiazines substituted at the 3 and 6 positions were synthesized by treatment of N-substituted N,N-bis(1H-1,2,3-benzotriazol-1-ylmethyl)-amines with thioamides and zinc bromide in dry CH(2)Cl(2) at room temperature for 48-60 h in 48-80% yields.     

Preparation of 3,4-dihydro-2H-1,3-benzoxazines

N,N-Di(butoxymethyl)alkylamines react with phenols under mild conditions to yield substituted 3,4-dihydro-2H-l,3-benzoxazines.