STEREO AND ELECTRONIC EFFECTS IN THE RHODIUM(II)-MEDIATED SYNTHESIS OF POLYCYCLIC LACTONES AND LACTAMS FROM ALPHA-DIAZO ESTER AND AMIDE PRECURSORS

The rhodium(II) carboxylate catalyzed decomposition of several alpha-d iazo esters and amides has been studied. A series of 5-keto-1-diazo ac etates were prepared by acylation of alpha-hydroxy ketones using the ( p-toluenesulfonyl)hydrazone of glyoxylic acid chloride. Treatment of t hese compounds with Rh(II) acetate afforded products derived from carb enoid insertion into solvent. When the hydrogen atom of the diazo carb on was replaced with an electron-withdrawing substituent, smooth cycli zation occurred to produce a carbonyl ylide dipole which was subsequen tly trapped with different dipolarophiles. A series of N-alkyl-2-diazo -3-oxobutylamides, when treated with a catalytic quantity of rhodium(I I) acetate, gave furo[3,4-c]furans in good yield. The reaction proceed s via addition of a rhodium-stabilized carbenoid onto the acetylenic p i-bond to give a vinyl carbenoid which subsequently cyclizes onto the neighboring carbonyl group to produce the furan ring. N-Alkynyl-substi tuted 2-diazoacetamides were also found to cyclize onto the tethered a lkyne unit. The resulting rhodium carbenoid can undergo intramolecular and bimolecular cyclopropanation depending on both electronic and con formational factors. Rotamer population of the starting diazoamide was also found to influence product distribution.