Conversion to gem

The one-pot conversions of oximes to gem-halonitro compounds have been achieved by using A(/V,/V.-trihalo-l,3,5-triazines,131 chloroperoxidase in the presence of hydrogen peroxide and potassium chloride,132 or commercial OXONE and sodium chloride.133 Of these methods, the case of OXONE may be the most convenient (Eq. 2.65). 

Marchand and co-workers ° synthesis of 5,5,9,9-tetranitropentacyclo[5.3.0.0 .0 °.0 ] decane (52) reqnired the dioxime of pentacyclo[5.3.0.0 .0 °.0 ]decane-5,9-dione (49) for the incorporation of the four nitro groups. Synthesis of the diketone precursor (48) was achieved in only five steps from cyclopentanone. Thus, acetal protection of cyclopentanone with ethylene glycol, followed by a-bromination, and dehydrobromination with sodium in methanol, yielded the reactive intermediate (45), which underwent a spontaneous Diels-Alder cycloaddition to give (46). Selective acetal deprotection of (46) was followed by a photo-initiated intramolecular cyclization and final acetal deprotection with aqueous mineral acid to give the diketone (48). Derivatization of the diketone (48) to the corresponding dioxime (49) was followed by conversion of the oxime groups to gem-dinitro functionality using standard literature procedures. 

Buncel et a/.33 have shown that 4,6-dinitro-7-methoxybenzofuroxan undergoes attachment of MeO" in MeOH at position 7, yielding the gem-dimethoxy adduct 189. No evidence has been obtained so far for the concurrent formation of other adducts, in contrast to the behavior of 4-nitro-7-methoxybenzofuroxan. Adduct 189 has been characterized by H-NMR in methanol solution. Its formation occurs in a fast, reversible process followed by slow conversion to the conjugate base of 4,6-dinitro-7-... 

Treatment of chroman-4-ones with PCI5 yields 3,4-dichlorochromenes. It is postulated that the reaction proceeds by initial a-chlorination, followed by conversion to the gem-dichloride. Dehydrohalogenation leads to the observed product. The chloroketone has been isolated from 2,2-dimethylchroman-4-one and phosphorus pentachloride (79TL3901). 

Attempted conversion of gem-dibromotriangulanes 68 and 71 to the corresponding vinylidene derivatives, e.g. 69 was also accompanied by an unusual rearrangement, yielding cyclobutene derivatives (equations 46 and 47). On the other hand, a similar reaction of dibromide 71 gave the desired allene 72 in 85% yield (equation 48). ... 

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