摘要:
To study a recently developed radical cyclization reaction followed by a fragmentation process in more detail, a series of a-benzoyl carbonyl compounds were prepared, including precursors with aldehyde and ketone moieties. Initiated by tributyltin hydride and AIBN, radical cyclizatiori followed by,fragmentation proceeded to give the desired. carbonyl-translocation products 4-benzoyl-5-pentanal, 4-benzoyl-5-pentanone, 5-benzoyl-6-hexanal, and 5-benzoyl-6-hexanone radical systems In comparison with,early-reports on radical cyclization reactions of alpha-oxy carbonyl compounds, neither a geminal dialkyl effect nor ,a conformationally rigid :system. was required to give the desired carbonyl translocation products This effect dearly proves that a benzoyl group serves as,a protecting group in these radical processes, which not only enhances cyclization efficiency but also increases the rate of the fragmentation step, eventually producing the desired carbonyl translocation products. These observations provide an alternative point of view in:the field of radical cyclization reactions. Since the fragmentation step could be enhanced by appropriately positioning an alpha-benzoyl group, these four radical processes could be used to convert the naturally occurring D-sugars, such as D-pentoses and D-hexoses, into rare deoxy-L-sugars. Furthermore, a cascade radical process involving radical cyclization and fragmentation followed by addition to the allyltin reagent was developed and is reported herein.