No abstract

No abstract

No abstract

If a diarylalkyne 4-XC6H,CzCR (R = Ph,,H,) or 1 -phenylpropyne in trifluoroacetic acid containing mercury( 11) trifluoroacetate is irradiated with U.V. light filtered through Pyrex glass, the e.s.r. spectrum of the corresponding azulene can be observed. The azulenes have been isolated and converted back into their radical cations by irradiation in trifluoroacetic acid, or in dichloromethane containing (4-BrC6H,),N+' or (2,4-Br, C, H, ), N +*.Possible mechanisms by which the azulenes are formed from the alkynes are discussed.

Gordon Street, London WCI H OAJ U maturated hydroperoxides ( R' R2CH 0,H ), 2-phenylpent-4-enyl hydro peroxide (1 ), 3-phenyl hex-5en -2-yl hydroperoxide ( Z ) , 5-methyl hex-5-en -2-yl hydroperoxide (3), cyclo-oct -4-enyl hydroperoxide (1 8), and cyclo-oct-3-enyl hydroperoxide (24) have each been prepared from the corresponding carbonyl compound ( R1R2CO) by the sequence: i, conversion to thep-tosylhydrazone ( R'R2C=N-NHTs); ii, reduction with sodium cyanoborohydride at pH 3.5 to give the N'-p-tosylhydrazine ( R1R2CH-N H-NHTs); and iii, oxidation with hydrogen peroxide and sodium peroxide. Isomerisation occurs in the preparation of the cyclo-octenyl hydroperoxides, particuarly if the pH falls markedly below 3.5 in the reduction step.Non-allylic alkenyl hydroperoxides are principal precursors of cyclic peroxides. Studies of the cyclisations, which occur under both radical and polar 3*5-8 conditions, contribute to an understanding of important processes such as lipid peroxidation and the oxidative degradation of rubber. The cyclic peroxides themselves serve as useful models for investigating the chemistry of naturally occurring substances such as prostaglandin endoperoxides. They also provide a convenient source of theoretically interesting diradicals, and have potential as intermediates in the stereocontrolled syntheses of polyoxygenated compounds. Certain &,&-unsaturated hydroperoxides are also precursors of gem-dialkylperoxonium ions which are a new, and as yet little studied, class of oxygen transfer rea g e n t ~. ~ With the single exception of 2-rnethylhex-5-en-2-yl hydroperoxide, which was prepared by silver(1)-assisted perhydrolysis of the corresponding bromide: all the non-allylic alkenyl hydroperoxides reported in the literature are primary or secondary and have been made by the perhydrolysis of alkenyl methanesulphonates under basic conditions. 1-8,10 We have found several examples where these reactions fail or afford hydroperoxides in only very poor yield. In an attempt to provide an alternative route to such hydroperoxides, we decided to investigate the use of the oxidation of N-alkenyl-N'-p-tosylhydrazines. The method is based on that applied by Caglioti and co-workers" to the preparation of a small number of saturated alkyl hydroperoxides (Scheme 1). This approach appears attractive in that high yields are reported for each of the three steps. However, the method has not found general use.