Generation of a ten-.pi.-electron carbocyclic aromatic carbene by a carbene-carbene rearrangement

Some Pericyclic Reactions of Carbenes

“…Of these, the first reported (Gebert et al, 1973) was the rearrangement of 82 to the 3,8-methano[10]annulenylidene (83) (see Scheme 6). Of these, the first reported (Gebert et al, 1973) was the rearrangement of 82 to the 3,8-methano[10]annulenylidene (83) (see Scheme 6).…”

Evidence for cyclopropene intermediates in the rearrangement of aromatic carbenes to arylcarbenes

“…The interconversion of aromatic and arylcarbenes is a notable exception to this generality. Besides detailed studies concerned with the conversion of phenylcarbene (5) and its derivatives to cycloheptatrienylidenes (1) in the gas phase1 and of benzocycloheptatrienylidene (20) to naphthylcarbene (26) in solution,12 a growing number of heterocyclic3•4 and nonbenzenoid6'6 carbenes have been shown to undergo a similar isomerization. Yet the mechanism of this reorganization remains a subject of considerable conjecture.7-11 Three suggested mechanistic alternatives are collected in Figure 1.…”

Synthesis and photolysis of 2-acylpyrazolidin-3-ones. Model for the photochemical syntheses of 6-azapenicillin isomers

“…l-(2,2,2-Trichloroethoxycarbonyl)-5,5-dimethylpyrazolidin-3-one (2). To a solution of 5,5-dimethylpyrazolidin-3-one (1, 23.0 g, 0.20 mol) in aqueous 2 N NaOH (100 ml) cooled to 10-20°u nder a nitrogen atmosphere was added dropwise 2,2,2-trichloroethoxycarbonyl chloride (42.5 g, 0.20 mol). After the addition was complete, the mixture was allowed to warm to room temperature and was stirred for 2 hr.…”

“…Heating of 3c (110°for 3 hr) followed by recrystallization of the crude product from Et^O resulted in a 48% yield (based on 2) of pure 4c: mp 81-82°; ir (CC14) 2970, 1740 (shoulder 1760), 1390, 1235, 1200, 1130, 1105, 1050 cm"1; NMR (CC13D) 1.24 (d, J = 7 Hz, 6), 1.59 (s, 6), 2.25 (s, 2), 3.65 (septet, J = 7 Hz, 1), 4.82 (s, 2); mass spectrum (70 eV) m/e (rel intensity) 358 (trace, 3-C1, M+), 288 (19, 3-C1), 273 (7.5, 3-C1), 253 (2, 2-C1), 211 (2.5), 169 (1.5), 149 (2), 141 (4.5), 131 (8, 3-C1), 113 (13), 99 (22), 97 (6), 95 (8), 83 (23), 82 (4), 71 (61), 61 (5), 56 (18), 55 (12), 43 (100), 41 (33). 5.5-dimethyl-3-pivaloxy-2-pyrazoline (3d).…”

“…Pyrazolidin-3-one 4e was converted into 5e in a manner similar to that described for the reaction of 4a to give 5a. Recrystallization of the crude product from Et20 gave a 64% yield of pure 5e: mp 62-63°; ir (CC14) 3260,2960,1750,1695,1420,1315,1275,1235,1165 cm-1; NMR (CCI3D) 1.29 (s, 6), 2.52 (s, 2), 4.20 (s, 2), 4.90 (broad s, 1, NH), 7.29 (s, 5); mass spectrum (70 eV) m/e (rel intensity) 232 (4, M+, this ion disappears rapidly with time), 214 (2), 149 (2), 118 (6), 115 (7), 114 (100), 113 (5), 100 (5), 99 (86), 91 (37), 83 (23), 72 (28), 71 (9), 65 (7), 56 (20), 55 l-Acetamido-4,4-dimethylazetidin-2-one (9a). From Irradiation of 5a.…”