Intramolecular Carbon-Hydrogen Insertions of Alkylidenecarbenes. 1. Selectivity

Article abstract of DOI:10.1021/jo00174a019

Base-promoted reaction between dialkyl ketones having γ-hydrogens and dialkyl (diazomethyl)phosphonates leads to formation of cyclopentenes in modest to high yields.The relative reactivity of various types of carbon-hydrogen bonds for the process, which involves insertion by an alkylidenecarbene, has been assessed, and the result has been compared to those reported when the carbene is generated by α elimination and by 1,2-shifts.The comparison suggests that a common species, viz., an alkylidenecarbene, may be responsible for formation of the cyclopentenes obtained from (a) flash vacuum pyrolysis of alkynes and (b) decomposition of diazoethenes, whereas that derived from α elimination of terminal vinyl halides is more selective, a result consonant with production of a carbenoid.