Steric Effects in Elimination Reactions. XII. The Reaction of Potassium t-Butoxide with Cyclic Tosylates. The Effect of Structure on the Rate and Direction of Eliminations in Cyclic Systems¹

Abstract

Rates and isomer distributions in the elimination reactions of potassium r-butoxide in r-butyl alcohol at 50°with representative cycloalkyl and rrazis-2-methylcycloalkyl tosylates were determined in order to examine this reaction as a suitable probe for structural effects in E2 reactions and to test the relative advantages of the electronic and steric theories in accounting for the results. The rates of the simple cycloalkyl tosylates reveal only a modest change in the second-order rate constants with ring size (k2 X 104 mole-1 sec-1): cyclopentyl, 7.81; cyclohexyl, 2.14; cycloheptyl, 2.34; cyclooctyl, 1.28. rra«i-2-Methylcycloalkanols were synthesized via the hydroboration of the 1 -methylcycloalkenes and the tosylates were subjected to elimination. The 99% 3-, 1 % 1-distribution in the first three members reveals stereoelectronic control requiring the usual trans coplanar arrangement of the atoms involved in the elimination stage. However, a 50-50 formation of the two olefins was observed in the cyclooctyl derivative, presumably a result of the greater flexibility of the eight-membered ring. Finally, the rates of elimination of rra/w-2-methylcyclopentyl (1.10) and -cycloheptyl tosylate (0.84) are only moderately slower than those of the parent compound, but the rate constant for the corresponding cyclohexyl compound, 0.024, is markedly depressed from the rate constant for the parent structure, 2.14. The slow rate in cyclohexyl system can be attributed to the energy required to place both the methyl and the tosyl groups in the axial position.

Mechanisms of elimination reactions. XX. Stereochemistry of photoeliminations from some cyclic phenylacetates

“…íran.s-2-MethylcycIooctanol was obtained by the hydroboration of 1-methylcyclooctene. 23 The product and its acid phthalate had properties in agreement with those in the literature,23•24 and glpc (see above) showed the alcohol to be the pure trans isomer.…”

Structure and Thermal Decomposition of Some 5-(Cyclohexyloxy)thianthreniumyl Perchlorates

“…We attribute formation of 6 to the inversion of configuration of 5b , placing the substituents in the diaxial configuration, eq 5. Inversions of this kind prior to product formation have been proposed by others, for example, to account for the formation of 3- methylcyclohexene in the relatively slow elimination reactions of trans -2-methylcyclohexyl tosylate. − The formation of trans -2-(ethyloxy)cyclohexanol from the solvolysis of trans -2-hydroxycyclohexyl tosylate has been attributed, also, to neighboring-group participation (i.e., backside attack) of the hydroxyl group in the tosylate . The preferred formation of 7 from 5c (eq 6) is also understandable.…”

“…Our work with 5d (trans ) and 5e (cis) can be compared with reactions of cis - and trans -2-methylcyclohexanol and their tosylates that are reported in the literature. Under purely E2-like conditions, the sulfurane from trans -2-methylcyclohexanol 21 and trans -2-methylcyclohexyl tosylate gave 99−100% of 3-methylcyclohexene ( 9 ). ,, Thermal decomposition of the trans -tosylate in dimethyl sulfoxide (DMSO), however, gave 70% of 1-methylcyclohexene ( 8 ) and only 30% of 9 , and the decomposition was said to have, therefore, carbonium-ion-pair character gave 8 and 9 in the ratio 66:34, that is, akin to the ratio reported by Hatch for the tosylate .…”

.alpha.'.beta. Elimination of carbanions derived from thioethers

“…After addition of water, the extraction was performed with chloroform. The (a-methylbenzyl) octadecyl thioether (3d) (95%) was recrystallized in methanol: mp [35][36] °C; >H NMR (CDC13) 0.89 (t, 3 ), 1.25 (32 ), 1.56 (d, J = 7 Hz, 3 H), 2.28 (t, J = 6.5 Hz, 2 H), 3.92 (q, J = 7 Hz, 1 H), 7.22 (5 H); mass spectrum M+ 390, m/e 375, 300, 285. Anal.…”

“…The stereospecifically deuterated cyclooctanols were prepared according to the published procedures: the trans /3-deuterated cyclooctanol from the epoxide of m-cyclooctene with lithium aluminodeuteride35 and the cis /3-deuterated cyclooctanol by deuterioboration and oxidation of m-cyclooctene. 36 The reaction of the corresponding mesylates with sodium benzylthiolate in hexamethylphosphoramide resulted in the labeled thioethers 6 and 7. We assume that this last res-ch2c6h5 The regioselectivity was studied for the carbanion from sec-butyl benzyl thioether (2b).…”