Tetrahedron Letters, Vo1.30, No.3, pp 301-304, 1989 0040-4039/89 $3.00 + .OO Printed in Great Britain Pergamon Press plc CYCLIC CARBONYL YLIDE FORMATION FROM THE RHODIUM (II) ACETATE CATALYZED REACTION OF l-DIAZOALKANEDIONES Albert Padwa,* Richard L. Chinn, Susan F. Hornbuckle and Lin Zhi Department of Chemistry, Emory University Atlanta, GA 30322 USA Abstract: Treatment of 1-diazoalkanediones with rhodium (II) acetate results in cyclization of the intermediate rhodium carbenoid to give a cyclic carbonyl ylide which readily undergoes bimolecular dipolar cycloaddition with various dipolarophiles. a-Diazoketones are valuable synthetic intermediates, with considerable utility in the 1 8 preparation of a variety of cyclic and acyclic organic molecules. - We have recently reported that the rhodium metal induced reaction of l-diazo-2,5-pentanediones in the presence of various dipolarophiles results in carbonyl ylide formation followed by 1,3-dipolar cycloaddition.9 Of the many unexplored questions concerning the factors that govern the formation of carbonyl ylides by this method, one that is very easy to formulate focuses upon the course of the reaction as a function of the length of the tether that links the carbonyl and diazoketone functionalities. Until now, the tether length has been restricted to cases where n=2 (i.e. 6-ring formation).ls In this communication, we report that a similar tandem cyclization-cycloaddition sequence occurs with both 5 and 7-ring cyclic carbonyl ylides. 0 zyxwvutsrqponmlkjihgfedcbaZ 0 ii Rc (CH,),COCHN, J R As a consequence of the ready availability of ketopinic acid,” 6-diazoketo-7,7- dimethylbicyclo[2.2.l]heptane (1) was the initial system selected for study. Treatment of 1 with a catalytic amount of rhodium (II) acetate at 25OC in benzene with dimethyl acetylenedicarboxylate (10% mol excess) afforded cycloadduct 2, mp 83-84OC, in 85% yield.12 The cycloaddition proceeded with complete diastereofacial selectivity. W e believe that approach from the a-face of the dipole is the preferred process as a consequence of the severe steric interaction with the bridgehead gem dimethyl group associated with P-attack. Similar treatment of 1 with methyl propiolate produced cycloadduct 3 in 72% isolated yield as the exclusive cycloadduct, mp 80- 8X.12 This result clearly demonstrates the high degree of regioselectivity possible in these reactions. In addition to the high facial and regioselectivity of the cycloaddition, diazoketone 1 also exhibits a high level of stereoselectivity. Cycloaddition of the metallocarbenoid derived from 1 was 301