Nonconcertedness of allylic cation promoted .pi.-cyclization reactions

Model studies of terpene biosynthesis. A stepwise mechanism for cyclization of nerol to .alpha.-terpineol

“…If, however, the cation is made too stable by additional alkyl substituents at C(l) and C(3), the reaction is stepwise, but stereorandom. 24 Finally, the intermolecular alkylation of dimethylallyl acetate by dimethylallyl cation, a system with no restraints on the orientation of the reactants, is stereorandom. 25 One should, therefore, anticipate a spectrum of mechanisms for biomimetic and enzymatic olefin alkylation reactions which depend on the nature of the electrophile and the double bond.…”

Solvolysis of 2-alkenyl-2-cyclohexenyl p-nitrobenzoates

“…The observed differences in reaction rate constants (Table I) of the compounds 6, 7, 13, and 15 NMRC 6 (H's, mult) 0 16.0 6.00 (C = 0), 6.13 (C=C) 3.20 (C=C-), 6.00 (C = 0), 6.12 (C=C), 10.01, 10.92 (HC=CH2) 5.40-6.12 (1 H, m, C=CH), 4.69-5.13 (2 H, m, C=CH2), 1.89 (3 H, s, C=CCH3), 1.71-2.50 (10 H) 24.3 6.00 (C=0), 6.12 (C=C) 4.83-5.30 (1 H, m, C=CH), 1.93 (3 H, s, C=CCH3), 1.67 (3 H, s, C=CCH3), 1.59 (3 H, s, C = CCH3), 1.46-3.0 (10 H) 0 All isolated yields from keto ester 8. b Neat. c CC14; internal standard, Me4Si.…”

“…c CC14; internal standard, Me4Si. 3.22 (C=C-H), 6.11 (C=C), 10.43, 10.97 (HC=CH2) 5.41-6.19 (1 H, m, C=CH), 4.70-5.17 (O-H), 3.22 (C=C-H), 4.66 (C-D), 6.10 (C=C), 10.62, 10.93 (HC=CH2) 5.42-6.11 (1 H, m, C=CH), 4.77-5.23 (2 H, m, C=CH2), 2.62 (1 H, s, OH), 1.63 (3 H, s, C=CCH3), 1.38-2.35 (10 H) r^x H 0 93.9 2.98 (O-H), 11.95 (C=C-H) 93.3 2.94 (O-H), 4.70 (C-D), 11.98 (C=CH) 4.87-5.33 (1 H, m, C=CH), 3.77-4.05 (1 H, br s, O-CH), 1.64 (9 H, s, C=CCH3), 1.34-2.30 (11 H) 4.87-5.30 (1 H, m, C=CH), 2.52-2.95 (1 H, br s, OH), 1.66 (9 H, s, C=CCH3), 1.32-2.40 (10 H) 0 All isolated yields. b Neat.…”

“…It was shown2"6 that the solvolysis of alcohols 1 in formic acid gave, after reduction of the resulting mixture with LiAlH4, preferentially syn-octalinols 2 and 3 (except in the case of lc, where none of 3c was found3). Johnson studied the solvolysis of alcohols la, lc, and Id and obtained evidence that suggested (but did not prove) that the ionization step preceded cyclization.2 5A similar conclusion was reached in the study of cationic cyclization of methoxy trienyne 4.7 The obtained results 12 6, R-CH=CH2 7, R-CH=CMe2 native that two concerted mechanisms (SN2 and SN2' reactions) occur at the same time, giving the same stereochemical result.…”

Silylene rearrangements in the reactions of recoiling silicon atoms with trimethylsilane

“…If, however, the cation is made too stable by additional alkyl substituents at C(l) and C(3), the reaction is stepwise, but stereorandom. 24 Finally, the intermolecular alkylation of dimethylallyl acetate by dimethylallyl cation, a system with no restraints on the orientation of the reactants, is stereorandom.25 One should, therefore, anticipate a spectrum of mechanisms for biomimetic and enzymatic olefin alkylation reactions which depend on the nature of the Atoms created in nuclear transformations are usually born as high-energy cations that have broken free from the molecules in which their parent atoms were covalently bonded.1 Before a recoiling atom can incorporate itself by its reactions in a new molecule, it must lose much of its initial kinetic energy in a series of collisions in which electron exchange and electronic transitions can also occur.2 Thus the interpretation of the results of hot-atom experiments can be complicated by the simultaneous presence of several different charge and electronic states of the reacting species.…”