1,8-Diazabicyclo azepine

Perfluorotetramethylthiadiphosphanorbornadiene and bis(trifluoromethyl) thiadiphosphole can be prepared by thermolysis of an adduct of methanol and hexakis(trifluoromethyl)-l,4-diphosphabarrelene with sulfur [113] (equation 23) Pyrolysis of the adduct of hexafluorinated Dewar benzene and phenyl azide results in ring expansion giving azepine, which photochemically yields an intramolecular 2-1-2 adduct, a good dienophile for the Diels-Alder reaction [114, //5] (equation 24) Thermolysis of fluonnated derivatives of 1,5-diazabicyclo-... 

Treatment of the Z-aldehyde 9 (R1 = R2 = H) with trifluoroacetic acid in dichloromethane at — 10 C, then with l,4-diazabicyclo[2.2.2]octane or /V,/V-diethylpyridin-4-amine, constitutes the first synthesis of 27/-azepine (10, R1 = R2 = H) which was isolated, with great difficulty and in very low yield (1 %), as a highly volatile, unstable oil, the structure of which was confirmed by high field H and 13CNMR spectroscopy.290 Similar treatment of the Z-alkenones 9a-d furnishes the thermally unstable (5)-2/7-azepines lOa-d in much higher yields.291... 

Addition of benzoyl chloride to 2.5-dimethyl-3,4,6-triphenyl-3//-azepine (13) in benzene in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) leads to elimination of hydrogen chloride and formation of the 2-methylene-l//-azcpine 14.117 All attempts to isomerize the methylene derivative to 1-benzoyl-2,5-dimethyl-3,4,6-triphenyl-l//-azepine under basic conditions failed. Analogous reactions can occur with 2,5-dielhyl-3,4,6-triphenyl-3//-azepine. 

Attempts to prepare 5-vinyl-5F7-dibenz[b,/]azepine by alkylation of 5i/-dibenz[b,/]azepine with 2-chloroethyl-p-toluenesulfonate followed by dehydrochlorination, or by direct vinylation with acetylene under pressure in toluene or in dimethyl sulfoxide, have failed.194 Also, 5H-dibenz[b,/]azepine fails to react with acryloyl chloride, although the 5-acryloyl derivative 8 (R = COCH = CH2 mp 122 — 123 C) has been prepared in 65% yield by condensing dibenz-azepine 5 with 3-chloroacryloyl chloride, followed by dehydrochlorination of the product with l,8-diazabicyclo[5.4.0]undec-7-ene in dimethyl sulfoxide at 80-90°C.194... 

Fourteen seven-membered ring compounds have been tritium-labelled by AcT, AdT or HTI methods165 including ( )3,3,5-trimethylhexahydroazepine—162, 2-oxohex-amethyleneimine (caprolactam)—163, l-aza-2-methoxy-l-cycloheptene—164, 1,4-dia-zacycloheptane (homopiperazine)—165, l,8-diazabicyclo-[5.4.0]undec-7-ene—166, 5H-dibenzo[6j/]azepine (iminostilbene)—167, 8-chloro-l 1-(4-methyl-l-piperazinyl)5//-... 

In the first part of the section on the pyrimido[l,2-a]azepines, the chemistry of 2,3,4,6,7,8,9,10-octahydropyrimido[l,2-a]azepine (8) (generally called diazabicyclo[5.4.0] undec-7-ene, or DBU) is treated in a separate subsection, since DBU has proved to be a useful reagent in synthetic organic chemistry and an important catalyst in the synthesis of macromolecules. Since the appearance of two early reviews (72S591 75MI5), the applications of DBU have rapidly increased because of its favorable nonnucleophilic, yet strongly basic, properties. It can therefore be applied for the preparation of even relatively sensitive molecules. Following this, the synthesis, reactions, physicochemical properties, and briefly the applications of further pyrimido[l,2-a]azepine derivatives are discussed. The treatment of the chemistry of the other pyrimidoazepines (2-5 and 7) follows an essentially identical pattern to that for the pyrimido[l,2-a]azepines. 

Of particular interest is the thermal decomposition of azepines, diazepines, and triazepines. 3,4-Benzo-l,7-diazabicyclo[3.2.0]hepta-3,6-dienes (236) were found to decompose at 180° with loss of a nitrile or hydrogen cyanide. The other products of the (2 + 2)-cycloreversion were highly unstable isoindoles and could not be isolated.296 A similar type of reaction has been proposed for the decomposition of 4,5-dihydro-3//-azepines27 and jV-methylazepines,301 but the corresponding bicyclic intermediates 240 and 263 have not been detected. The question whether these cycloreversions are thermal or photochemical reactions remains unresolved. 

Methyl 3,6-di-t-butyl-l/7-azepine-l-carboxylate reacts with ethyl azidoformate to give a mixture of the 2,6-diazabicyclo[3.3.0]octa-3,7-diene (29) in 30% yield, together with a smaller amount of the 2,8-diazabicyclo[3.2.l]octa-3,6-dienes (30) and (31) (Scheme 3) <83TL2275>. The initial step is assumed to be nitrene addition to the 4,5-double bond of the azepine (Scheme 3), although it is possible that (30) may also arise by direct 1,4-addition. If the reaction is carried out with N-toluenesulfonyloxyurethane as nitrene source, (30) is the main product. Similar studies showed that... 

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