Trans- s. Geospecificity

Isomers s. a. Oximes, Stereoisomers cw,trans-isomers s. Geospecificity, CIS- and trans-Oxido compounds Isonitrile dihalides... 

A soln. of the startg. m. and 4 equivalents ketal heated ca. 8 hrs. at 100° in toluene containing 2,4-dinitrophenol as catalyst, and the intermediate ketone treated at 0° with NaBH4 in methanol > product. Y up to 81% purity 98%. -This olefinic ketal Claisen reaction is useful for preparing trans-disubst as well as trans-trisubst. olefinic bonds. The above producure is the last of a succession of 3 similar steps. F. e. and catalysts s. W. S. Johnson et al., Am. Soc. 92, 4463 (1970) Proc. Natl. Acad. Sci. U.S. 67, 1462, 1465, 1810, 1824 (1970) geospecific synthesis of ethylene derivs., review, s. J. Reucroft and P. G. Sammes, Quart. Rev. 25,135 (1971). 

Geospecific replacement. 1-Octyne and catecholborane stirred 2 hrs. at 70° under Ng, cooled to room temp., and stirred 2 hrs. at 25° with water -> frans-l-octenyl-boronic acid (Y 90%) dissolved in ether, cooled to 0°, aq. 3 N NaOH added followed at 0° by 20% excess iodine in ether with stirring, which is continued 0.5 hr. at 0° -> trans-l-ocitnyX iodide (Y 80%). Overall Y 71%. F. e. s. H. C. Brown, T. Hamaoka, and N. Ravindran, Am. Soc. 95, 5786 (1973) also cis-a,p-ethylenebromides with inversion of configuration s. ibid. 95, 6456 cis- and trans- ,/ -ethylenehalides via enesilanes cf. R. B. Miller and T. Reidienbadi, Tetrah. Let. 1974, 543. 

Palladium(II) salts such as dichlorobis(benzonitrile)palladium catalyze transetherification of enolethers at low temp. e. g. -30°. The reaction is geospecific with inversion, giving trans- from cw-isomers and vice versa. E. s. J. E. McKeon, P. Fitton, and A. A. Griswold, Tetrahedron 28, 227 (1972). 

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