Z%naary: Treatment of aliphatic ketones with ethyl diazoacetate in the presence of a catalyst results in the regio-and (where appropriate) diastereoseleotive forn'etion of en01 ethers which arise by an intramolecular 1,4-hydrogen shift from an intermediate oarbonyl ylide.
Since our original observations that the en01 ethers produced as a result of CuCl catalyzed decanposition of ethyl diazmcetate in the presence of 2-methylcyclohexanone and 3n-ethyl-2-butanone were formed with a high degree of regioselectivity,' we have determined both the regioselectivity and diastereoseleotivity in a number of unsynnetrical acyclic ketones and have developed a mechanistic model to explain the results. The reactions outlined in Schane I provide the opportunity to explore many mechanistic features of the ccmnparatively rare 1,4-simtropic shift of hydrogen.'-' The initial production of carbenoid 2 frcsn catalyzed decanposition of ethyl diazoacetate (1),5 followed by electrophilic attack on ketone 3 and 1.4-sign-etropic shift of hydrogen, leads to the product en01 ether(s). l/i-H-4 RCH=C(R')OCH,CO,Et 5
We have shown that the latter process is indeed an intramolsculareventby theobservation that an excess eguirnolar mixture of ketones 6 and 7 results in only undeuterated en01 ether 8 and specifically tetradeuterated en01 ether 9 with a ratio of 0.96 *0.056