Über kolloidales Palladium. Partielle und totale Hydrogenisation von Phenyl‐acetylen, Tolan und Diphenyl‐diacetylen

A new diene synthesis via organopalladium chemistry

“…Hydrolysis (CH3OH, H2O, TsOH, 60 °C) produced 8. NMR and VPC confirmed the presence of two compounds (78:22, E,E/Z,E) with the 10,11 double bond being E in both.15 Crystallization from pentane produced pure codlemone (8), mp 27.5-28.5 °C (lit.12 mp 28 °C), whose spectral properties agree with those reported.…”

“…Precursor 9 when subjected to the same conditions produced 10 contaminated by -10% Z,Z isomer. Hydrolysis, as above, gave pure bombykol (11) after TLC separation whose properties agree with those reported.13 NMR analysis at 270 MHz confirmed the Z,E stereochemistry as well: 5.29 (dt, J = 10.8, 7.5 Hz), 5.64 (dt, J = 15.0, 7.5 Hz), 5.94 (ddt, J = 10.8, 10.8, 1.5 Hz), 6.30 (ddt, J= 15.0, 10.8, 1.5 Hz).…”

“…The stereochemistry of the double bond originally present in the precursor remains unaffected as illustrated in the synthesis of the insect sex pheromones codlemone (8)12 and bombykol (11).1314 In the former case, reaction of 6 (diastereomeric ratio 1.3:1) with 3 mol % of catalyst at room temperature, 85 °C in PI1CH3, or reflux in THF led to 7 in 77-82% THRO' OAc co2h >c2h¡,,n 'bo'WvAAA…”

The Addition of Hydrogen to Multiple Carbon-Carbon Bonds.

“…Palladium black likewise does not bring about selective hydrogenation to the olefin (41,356). With colloidal palladium, on the other hand, reduction is selective in the large majority of cases studied, and when one molar equivalent of hydrogen has been added, the product is largely or entirely the olefin (41,42,44,45,123,161,163,197,230,280,345,350,353). There is, apparently, but one general exception to this rule: Lai (181) was unable to obtain any selective hydrogenation of acetylenic bromides of the type RC=CCH2Br, and the triple bond was always saturated.…”

“…The stereochemical course of the hydrogenation of disubstituted acetylenes and certain olefins has been of considerable interest because of its connection with the mechanism of catalytic hydrogenation. Early work by Paal (230) and by Kelber and Schwartz (161) indicated that the hydrogenation of such substances as phenylpropiolic acid and tolane by hydrogen in the presence of colloidal palladium led to the pure cis olefins, whereas reduction by chemical meth- ods formed the trans isomers. Later work, however, of Zalkind and his students on acetylenic glycols (345,348,351), of Williams and James (325) on acetylenedicarboxylic acid and tolane, and of Ott and his coworkers (228,229) on acetylenic acids and tolane, seemed to show that the reaction was not so simple, and that varying mixtures of cis and trans olefins were produced.…”