Radicals, reduction structure

The selenium analogues of these 1,3,2-dithiazolyl radicals have not been extensively studied. Benzo-l,3,2-diselenazolium perchlorate 28 can be prepared from 27 in an analogous fashion to the corresponding sulfur compound55 and its structure determined by X-ray structure analysis. Unlike BDTA (1,3,2-dithiazolyl radical), reduction of 28 afforded an unstable neutral radical. No stable selenium analogues have yet been isolated (Scheme 8). 

Simple radicals derived from aldoses have been considered exclusively in the preceding sections, from the point of view of structure and transformation. Application of radical reduction to tertiary anomeric radicals, produced from ketoses, higher sugars and other substituted analogues, and having generally alkoxy and... 

Briggs et al. proposed a new strategy for the synthesis of tricyclic structures using acyl xanthates as precursor for acyl radicals [121]. Irradiation with visible light of a solution of acyl xanthate in presence of 1,6-diene 126 afforded czs-fused bicyclic compound 127 in a good yield (Scheme 38). Radical reduction of xanthate and subsequent aldol condensation leads to the formation of [5.5.5]-fused ring systems similar to those of the triquinane terpene family. 

The complementarity of the method to base-catalyzed addition is further exemplified by the enoate 4. When the two-step protocol involving bromomethoxylation/radical reduction was applied, both the cis- and trim-products O.v-5 and tram-5 were obtained17. As shown previously (Section 4.7.1.1.1.2.1.), base-catalyzed addition of methanol to structurally closely related enoates afforded exclusively trim-addition products. 

To decide between these two models, they compared rate-structure profiles for the disappearance of alkyl halides in contact with magnesium with rate-structure profiles for others models of reduction. These included (1) rate-structure profiles for the free radical reduction of alkyl chlorides with tri-M-butyltin hydride in diethyl ether [33], assuming... 

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