Cyanoketenes. Synthesis and cycloadditions to formimidates

Abstract

We have previously reported that p-azido-a-chloroy-methoxy-A aT lF-crotonolactone (la) undergoes thermolysis in refluxing benzene to give chlorocyanoketene (2%) and methylformate. 1Reported here is the observation that the corresponding a-bromo-and a-iodo-analogs ofA under-

Cycloadditions of cyanoketenes to cinnamylidenamines and benzylidenamines. Synthetic scope, stereochemistry, and mechanism

“…In this case, the observed products were the /3-lactam 27 and the twolactams 28 and 29. The stereochemistry of 27 was readily assigned by the declorination/methylation sequence outlined in Scheme XI. That is, methylation of the enolate 30 from the least hindered face gave only the /3-lactam 27.…”

“…The organic layer was dried and the solvent removed in vacuo. The residue was subjected to preparative thin-layer chromatography (silica gel, 1:9 ethyl acetate-hexane) to give 55 mg (60%) of the titled mixture of diastereomers in a ratio of 1:1: colorless oil; IR (neat, cm"1) 2245,1765; NMR (CDC13) 7.40 (s, 5 ), 7.20 (m, 4 ), 6.90 (m, 1 ), 6.30 (m, 1 H), 4.85 (m, 1 H), 4.45 (d, J = 5 Hz, 0.5 ), 3.90 (d, J = 3 Hz, 0.5 H), 3.75 oxyphenyl)-3-methyl-4-(2-phenylethenyl)-2-azetidinone (27) and (Z)-and (£)-3-Cyano-3,4-dihydro-l-(4-methoxyphenyl)-3-methyl-4-phenyl-2(lfl')-pyridone (28 and 29). A solution of 120 mg (0.55 mmol) of 2,5-diazido-3,6-dimethyl-l,4benzoquinone and 237 mg (1.0 mmol) of 11c in 10 mL of anhydrous chlorobenzene was maintained at 130 °C for 1 h. The solvent was then removed and the dark brown residue subjected to PLC (silica gel, 1:9 ethyl acetate-hexane) to give the purified products 27 and 28.…”

Conjugated ketenes: new aspects of their synthesis and selected utility for the synthesis of phenols, hydroquinones, and quinones

“…For example, 4-azido-3-chloro-5methoxy-2(5H)-furanone (16) smoothly cleaves to chlorocyanoketene (19) and methyl formate in refluxing benzene. 21 In a related fashion the azidomaleic anhydride 17 and 3-azido-4-chlorocyclobutendione (18) have also been observed to give chlorocyanoketene. 22,23 The conversion of 18 to 19 is of particular note since this takes place at temperatures as low as -30 °C when the azidocyclobutenedione is generated from 2,3-dichlorocyclobutenedione upon treatment with sodium azide in acetonitrile.…”

Catalyst‐Free Synthesis of Diastereomerically Pure 3‐Cyanoazetidin‐2‐ones via Thermally Promoted Tandem Wolff Rearrangement–Staudinger [2+2] Cycloaddition

“…[13,14] An alternative, though practically less convenient and less general approach, is the thermal decomposition of various azides (Scheme 2b). [15][16][17][18] Finally, thermally promoted ring contraction of 4-azidopyrrolinones also provides a way to obtain 3-chloro-3-cyano-β-lactams (Scheme 2c). [16] And if the Staudinger [2 + 2] cycloadditions reported in the literature generally suffered from moderate yields, the latter two approaches (apparently limited in scope) required handling of potentially explosive azides.…”