4) De Vries, L. J. Am. Chem. SOC. 1978,100, 926. (5) Kosower, E. M.; Waits, H. P.; Teuerstein, A.; Butler, L. C. J. Org. Chem. 1978,43,800. (6) A special effect on polysubstituted radical stabilization has been first suggested by theoretical argument by (a) Dewar, M. J. S. J. Am. Chem. SOC. 1952,74,3353 and then observed experimentally and termed 'push-pull stabilization by (b) Balaban, A. T. Rev. Roum. Chim. 1971, 16,725 and "meroetabilization" by (c) Baldock, R. W.; Hudson, P.; Katritzky, A. R.; Soti, F. J. Chem. SOC., Perkin Trans. 1 1374,1422. See also: (d) Aurich, H. G.; Deuschle, E.; Weiss, W.

Dedicated to the double anniversary: 100 years Wurster's salts and SO years Paneth's radical reactions with metal mirrorsThe 100 years old Wurster's salts have long been recognized as compounds with radical cations. Their unusual stabilization derives partly from capto-dative (cd) substitution. This principle is now discussed as one factor of radical stabilization and it is applied to simple methine derivatives. cd-Substitution has synthetically useful applications: cd-substituents on a carbon atom allow its selective dehydrodimerization. Olefins with geminal and thus cross-conjugated cd-substituents are "radicophilic" and permit twofold carbon radical addition. cd-Substituted olefins are useful antioxidants, polymerization inhibitors and are promising agents in the control of biological radical reactions. Generally, many reactions of cd-substituted molecules appear to involve radicals.Angew. Chem. Int. Ed. Engl. 18, 917-932 (1979) 0 Verlag

Abstract

SummarySome (1-and 8-halonitrosoalkenes 1 have been synthesized and characterized. The halogen atoms of the oxime precursors 2 can be substituted by alkoxy groups. Two kinds of cycloaddition reaction of 1 have been observed: i) reaction of the NO group with dienes gives 3,6-dihydrooxazine derivatives 6 which isomerise to epoxyepimines 7 in most cases of 8-substituted nitrosoalkenes: ii) if 4,5-dihydrooxazines 22 are obtained, the cycloaddition of the nitrosoalkenes as 4 7r-component is presumed.Nitrosoalkenes possess a large synthetic potential, since they comprise both an alkene activated by an electron withdrawing group and an 1,3-diene system. Furthermore, the nitroso group itself reacts with it wide number of reagents [l] and allows an easy, simultaneous incorporation of nitrogen and oxygen by addition We have recently reported the epoxy-epimination of cyclic 1,3-dienes by isomerization of the cycloadducts formed from such dienes with certain halonitrosoalkenes [6] [7]. This reaction merits particular attention since nitrosoalkenes are readily accessible, highly reactive intermediates which can be used in situ. In order to study the scope and limitations of this stereospecific reaction, which allows the functionalization of the four sp2-centres of a diene in one step, it seemed interesting to vary the dienes and the substituents of the nitrosoalkene.') Taken in part from the Ph. D-Thesis of E. Francotte (l078), present address: C'iha-Geigy AG, Zentrale Forschung. CH-4002 Basel.0018-019X/81/4/1208-11$01.00/0 0 198 I Schweizer-ische Chemiache Gesellschaft