Compounds (1)-(4), 3,3-disubstituted diazirines having a carbonyl group at a position a to the three membered ring, have hitherto been synthesized by oxidation of the corresponding alcohols (a-azicycloalkanones ( l ) ) [ '~, or more frequently by photoisomerization of a-diazocarbonyl compounds, (3H-diazirinecarboxylic acid dialkylamides (2)I2J, Nalkyl-3-azi-2-indolinone (3)131, isopropylidene-3,3-diazirinedicarboxylate (4)l4l).All attempts to photocyclize diesters and amidoesters of diazomalonic acid have been unsuccessful due to the spontaneous isomerization of the diazirines (5) to the educts. This has been attributed to the steric effects of the two carbonyl substituents1'1. Indeed, within a few weeks, (4) undergoes spontaneous isomerization at room temperature to the diazo compound[4'. This fact, the low thermal stability of the spiranes (1) n=4I'l and (3) ['), and the lability of (1) in acidic media"] may be attributed to the favorable interaction (pseudoconj~gation~~l) between the diazirine ring and the C --=O group in the five and six membered rings. (cf. spiro-activationl5l). We therefore believed that a study of the synthesis of diazirines (S), with conformationally mobile C==O groups, would provide a route to their stable derivatives.We have found that the 3,3-diazirinedicarboxylates (9) are readily accessible by reaction of the tosyloximes (6) with 0-alkylhydroxylamines161 or by oxidation of the 3,3-diaziridinedicarboxylic dimethyl ester (7) with tert-butylhyp~chlorite['~. The esters (9), thus obtained, are colorless and stable at 0 "C; after being stored for a month at 20 "C, crystals of (9a) were "0zCMeOzC H02cXii N unchanged and a solution of (9a) in trifluoroacetic acid was unchanged after 2 hours ('H-NMR investigation). Mild amidation and alkaline hydrolysis of (9a) (0 to -5°C) yielded the monamide ( l o ) , which was stable at 0 "C, and the salts (8) and (12) respectively. While crystals of the dipotassium salt (12) were also unchanged after storage for two months at 20 "C, the monopotassium salt (8) decomposed within a few hours at 0°C. Both salts exploded when triturated! The monoacid (11) and diacid (13) are colorless stable crystalline substances at 0 "C; the structure of (13) was confirmed by conversion to the diesters (9). The UV-spectra of a11 the diazirine products obtained displayed a shoulder around the 240-250 nm region and a band at 286-300 nm (see Table 1). We have assigned this band to a n+n* transition@], since its position was almost identical in the esters (9), amide (lo), and acids (11) and (13). Furthermore when methanol was substituted for heptane as solvent, and when HClO, was added to a solution of (9a) in methanol, no hypsochromatic shift was observed. compounds (8) . (On). (96). (10). ( / I ) , 112). and (13). Comp