Generation of allenyliodinanes and their reductive iodonio-Claisen rearrangement

TLDR: This is the first to show that meta-Claisen rearrangement occurs preferentially even when a free para position is available, and can be interpreted in terms of the small bond energy of the breaking apical carbon-iodine (III) bond.

Abstract: Reported for the first time are the generation of allenyliodinanes and their reductive iodonio-Claisen rearrangement Reaction of propargylsilanes, germanes, and stannanes with aryliodinanes in the presence of BF 3 -Et 2 O undergoes a reductive iodonio-Claisen rearrangement under mild conditions, yielding o-propargyliodoarenes in good yields The reductive ortho propargylation probably involves the intermediate formation of allenyl(aryl) iodinanes, which undergo [3,3]-sigmatropic rearrangement The lack of crossover products argues for the intramolecularity of the rearrangement When both ortho positions of aryliodinanes are occupied with alkyl substituents, the reductive iodonio-Claisen rearrangement affords meta substitution products This is the first to show that meta-Claisen rearrangement occurs preferentially even when a free para position is available The reductive ortho propargylation of iodinanes takes place under much milder conditions than the Claisen rearrangement The lower activation energy associated with the iodonio-Claisen rearrangement of allenyl(aryl) iodinanes can be interpreted in terms of the small bond energy of the breaking apical carbon-iodine (III) bond