Syntheses and photochemistry of eight-membered cyclic azo compounds

Abstract

The preparation of the cis and trans isomers of 3,8-dimethyl-c«-l,2-diaza-l-cyclooctene (1 and 2, R = CHs) and the synthesis of cis-1,2-diaza-1 -cyclooctene (3) are described. The irradiation of these compounds and of /rani-l,2-diphenyl-cz's-l,2-diaza-l-cyclooctene (2, R = C6H5) in the presence and in the absence of triplet sensitizers is also discussed. In all cases, differences in the amounts of disproportionation and coupled products were noted when product distributions observed in the sensitized reactions were compared with those of the nonsensitized photolyses. These variations in product ratios were rationalized in terms of spin-correlation effects.Recently, there has been considerable interest in the .(1) This is the 47th in a series of papers concerned with the preparation and decomposition of azo compounds. For the previous paper, see

Complete determination of the stereochemistry of a 3,5-dialkylpyrazoline thermal decomposition. Synthesis, absolute configuration, and pyrolysis of (+)-(3R,5R)- and (+)-(3R,5S)-3-ethyl-5-methyl-1-pyrazolines

“…tantalum wire column. The product was distilled at reduced pressure through a 6-in. Vigreux column to give 161.6 g of the alcohol (86.6% yield; bp 63-65 °C (50 mm)): IR 3570, 3400 (br), 3075, 2960, 2920, 2880, 1640, 1440, 1000, 995, and 920 cm-'; NMR (CC14) 0.93 (t, J = 6.5 Hz, 3 H, -CH2CH3), 1.38 (q, 2 H, -CHOHCtf2CH3), 1 -73 (s, 1 , OH), 2.0-2.3 (m, 2 H, =CHCH2~), 3.48 (quintuplet, 1 H, -C//OH), 4.S-5.2 (m, 2 H, vinyl CH2), S.4-6.2 (m, 1 H, vinyl CH). Anal.…”

“…The thermal and photochemical decomposition of azo compounds (1) is a clean and general method of producing2 a wide variety of organic free radicals (2). Analogously, many cyclic azo compounds (3) decompositions extensively investigated3 as a means of generating various types of biradicals (4). Two questions central to studies of the mechanisms of the 3 -*• 4 reaction have been:…”

“…For cases in which n> 2, the mechanism of decomposition is reasonably well understood and appears to parallel those of acyclic systems-i.e., the simultaneity of C-N bond cleavage depends to some extent upon the level of substitution at the -carbon atoms, and the intermediate ultimately generated exhibits the sort of chemical behavior one expects of a methylene chain having classical free radical character at each terminus. 4 The n'= 2 case has presented something of a problem due to the propensity of six-membered azo compounds to rearrange to hydrazones by catalyzed hydrogen transfer; however, it has recently been demonstrated that the chemistry of these systems is well accounted for by assuming that they decompose partly by a concerted mechanism and partly to an intermediate which is identical with that produced on thermolysis of the corresponding cyclobutanes. 5 In contrast to the progress made during the past few years in understanding the decomposition of acyclic and large-ring cyclic azo compounds, the situation with regard to five-membered azo compounds (pyrazolines, 5) has remained seriously confused.…”