The preparation and fate of cubylcarbinyl radicals

Article abstract of DOI:10.1021/ja00020a035

The cubylcarbinyl radical has been generated from cubylcarbinyl bromide and from the N-hydroxy-2-pyridinethaione ester of cubylacetic acid under various conditions favoring hydrogen-atom transfer to the radical. Only when selenophenol in high concentration is used as the hydrogen donor is any methylcubane formed. Otherwise the cubylcarbinyl radical rearranges. There is no evidence of a 1,2-shift into the homocubyl system. Instead, one, two, or three bonds of the cubane nucleus cleave, leading to a variety of olefinic products. For the most part, these have been characterized. A mechanistic scheme accounting for their formation is presented; sequential σ-bond breaking occurs regioselectively, favoring processes in which there is good overlap between the radical orbital and that of the breaking bond. The distribution of products is shown to depend qualitatively on the time the radical intermediates are let live, that is, on the concentration and effectiveness of the hydrogen atom transfer agent. From product distributions, the rate constant for ring cleavage of cubylcarbinyl radical is calculated to be at least 2 × 10¹⁰ s^-1, substantially greater than that of any radical derived to date from a saturated hydrocarbon system. Methodology is given for the synthesis of cubylcarbinol, cubylacetic acid, 1,4-bis(hydroxymethyl)cubane, methylcubane, and a variety of other new cabane compounds.