Sir :Moyer discovered that lY2,4-tribromobenzene, on exposure to excess potassium t-butoxide (t-BuO-K+) in 50 % t-butyl alcohol-50 % dimethyl sulfoxide (DMSO) at 53", suffered reductive loss of the 2-bromine. p-Dibromobenzene was formed in 70%.yield, and the bromine removed appeared as bromide ion. We have studied this unusual reaction and obtained evidence indicating its mechanism. h r Br 70 % A number of chloro, bromo, and/or iodo derivatives of benzene are partially and selectively dehalogenated by this reagent. In general, protodehalogenation occurs only at sites ortho to other halogen atoms and is most facile for halogens flanked on both sides by ortho halogens. Other things being equal, deiodination occurs more readily than debromination, while dechlorination has not been observed. Electron-attracting substituents facilitate the reaction. Representative yields are 99 % m-dibromobenzene from 1,2,3-tribromo-(1) C. E. Moyer, Jr., Dissertation, Brown University, 1964; Dissertotion Abstr., 25, 4412 (1965).
The major product from the photoreaction of 4-methylenedispiro[2,1,2,3]decane (5) with Fe(CO), is shown to be a tricarbonyliron a,n-complex of structure (7), whereas the products from Pmethylenespiro[2,4]heptane (9) and 4-methylenespiro [2, Bloctane (15) are the respective bi-cyclic enones (12)-(13) and (16). OUR study of the thermolysis' and photolysis3 of vinylcyclopropenes in the presence of Fe(CO), has indicated that the small ring may be cleaved via two distinctly different reactions; (a) the Fe(CO),-induced metal insertion into a CH, + Fe(COI, (31 strained o-bond coupled with hydrogen migration to provide diene-Fe(CO), n-complexes [(l) + (2)]; (b) thephoto-induced cycloinsertion of carbon monoxide across the 'homodienic system' to yield cyc1ohexenones.i The only example in which these two reactions take place con-currently is that of 1, 1-dicyclopropylethylene (1), which on on thermolysis with Fe(CO), gives rise to a 1 : 1-mixture of (2) and (4)Ibs4 and on photolysis yields predominantly the cyclohexenone (4) product. Since the n-complex (2) is inert
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