The reaction of 3-ethynyl-2,2,4,4-tetramethyl-3-pentyl acetate (5) with potassium zerf-butoxide and olefins gave di-zerz-butylvinylidenecyclopropanes. The relative rates of reaction of the intermediate di-zm-butylvinylidenecarbene with olefins were determined and compared with previously obtained rates of reaction of the dimethylvinylidenecarbene. Arguments are presented which suggest that the carbenes are uncomplexed in the transition state of addition to olefins. Tetra-zerz-butylbutatriene and -hexapentaene were synthesized. Cycloadditions to the latter occurred across the central double bond-probably by way of a thermally accessible diradical of the cumulene. Dimerization of the hexapentaene gave tetrakis(di-zerz-butylvinylidene)cyclobutane-a stable cyclobutane deriva-
Notes lactone 3 and the dithiolactone 12, it was dissolved in methanolic sodium methoxide, cooled, diluted with water, and acidified. The crude 5 thus obtained was dissolved in 5% sodium carbonate, the insoluble fraction was removed by filtration, and the solution was extracted with ether. Acidification gave pure 5, which was dissolved in 50 ml of methanol and refluxed for 35 min to give 1.5 g of 7 as long yellow needles: mp 175-176.5°; ir (Nujol) 5.6, 5.9, 6.2 µ; nmr (CDCla) 7.30 (m, 6, phenyl ), 7.80 (m, 4, phenyl H); mass spectrum m/e 306 (M + ), 278, 250.
Aikenylidenecyclopropanes have been synthesized in moderate yields by reactions of derivatives of ethynylcarbinols with base in the presence of olefins.Evidence for the formation of diarylvinylidene carbenes as intermediates in the formation of tetraarylhexapentaenes is given.A faction scheme involving 7-elimination to give alkenylidene carbenes is proposed.
Carbon disulfide reacted with electron-deficient acetylenes to generate 1,3-dithiolium carbenes which formed compounds 1, 2, and 3 from hexafluoro-2-butyne and 6, 7, and 21 from dimethyl acetylenedicarboxylate. The 1,3-dithiolium carbenes were intercepted with alcohols to form 2-alkoxy-l ,3-dithioles and with phenols to form hydroxyaryldithioles. Aliphatic aldehydes and ketones produced acylmethylenedithioles. Aromatic aldehydes gave aroyldithioles. Olefins and carboxylic acids were also incorporated into the reactions and the products were identified. The heterocumulenes carbonyl sulfide and diisopropylcarbodiimide reacted differently
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