The preparation and fate of cubylcarbinyl radicals
摘要:
The cubylcarbinyl radical has been generated from cubylcarbinyl bromide and from the N-hydroxy-2-pyridinethione 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 sigma-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 X 10(10) 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 cubane compounds.
Enantioselective synthesis of (<i>R</i>)-2-cubylglycine including unprecedented rhodium mediated C–H insertion of cubane
作者:Sevan D. Houston、Benjamin A. Chalmers、G. Paul Savage、Craig M. Williams
DOI:10.1039/c8ob02959h
日期:——
The first enantioselectivesynthesis of (R)-2-cubylglycine, an analogue of (R)-2-phenylglycine in which the phenyl ring has been replaced by cubane, is disclosed. The key step was a telescoped Strecker reaction using (S)-2-amino-2-phenylethanol as a chiral auxiliary. Exploration of an alternative synthetic approach resulted in unprecedented cubane C–H insertion.