The tricarbonylchromium template for stereocontrol in radical reactions ofarenes

Chromium tricarbonyl complexed aryl aldeyhydes and ketones underwent Sm(II) -promoted radical lactone formation in the presence of alpha,beta -unsatura ted esters to produce diastereomerically pure lactones in good yields. The completely diastereoselective lactone formation involves capture of the ben zylic ketyl radical by the eater anti to the chromium tricarbonyl moiety. T he relative stereochemistry of the lactone and chromium tricarbonyl moietie s was proven by X-ray crystallography and supports the proposed mechanism. Enantiopure chromium tricarbonyl complexed arenes afforded single enantiome rs when subjected to Sm(II)-promoted radical lactone formation condiditions . The enantio- and diastereomerically pure chromium tricarbonyl complexed l actones were subsequently treated with BF3. OEt2 to generate a mixture of d iastereomers via Lewis acid promoted chromium tricabonyl directed cationic rearrangement. The diastereomers were separated and individually decomplexe d with I-2 to afford both of the corresponding chromium-free enantiomerical ly pure lactones starting from a single enantiomerically pure chromium tric arbonyl complex.