Silylated cyclohexadienes as new radical chain reducing reagents: preparative and mechanistic aspects

Various silylated 1,4-cyclohexadienes are presented as superior tin hydride substitutes for the conduction of various radical chain reductions. Debrominations, deiodinations, and deselenations can be performed using these environmentally benign reagents. Furthermore, Barton-McCombie-type deoxygenations using silylated cyclohexadienes are described. Radical cyclizations, ring expansions, and Giese-type addition reactions with the new tin hydride substitutes are presented. The polymerization of styrene can be regulated using silylated cyclohexadienes. Rate constants for hydrogen atom abstraction from two 1-silyl-cyclohexadienes by primary C-radicals were determined. The effects of the cyclohexadiene substituents on the reaction outcomes are discussed. Finally, qualitative EPR experiments on silyl radical expulsion from silylated cyclohexadienyl radicals are presented.

Radicals generated by bone cutting and fracture

When bone fractures, a remarkably high yield of radicals is generated. By working at 77K, these are stable enough for detection and study. Major species have been identified by ESR (EPR) spectroscopy as alkyl peroxyl radicals and RCH2. radicals. Also, a species thought to be O.- radicals, formed in the mineral phase, was detected in relatively low yield. It is suggested that as a break is generated, the mineral crystallites separate at grain boundaries with no major chemical damage, but that the tightly bound collagen strands running through the mineral phase are forced to break homolytically. Some probably react together, others react with oxygen, while the remainder are trapped in their primary form. The characteristic hyperfine triplet is assigned in part to RCH2. radicals from glycine units, which constitute about one-third of the total amino acid components in collagen, and in part to RNHCO radicals. The possible significance of the formation of active radicals during bone fracture is discussed.