Reactivity of Some Tertiary Chlorides with Methoxy and Olefinic Neighboring Group

Solvolysis rates of tertiary chlorides 1-6 and their hexadeuterated analogs 1-dg-6-đe were measured in ethanol (q> = 80%) and 2,2,2- trifluoroethanol (w = 97%). The (5-deuterium KIE calculated showed that chloride 1 solvolyzes with n-participation of the methoxy group in the rate determining step, while chloride 2 solvolyzes mainly by way of a kc process. Based on the reduced P-deuterium isotope effect, it was also concluded that in the solvolysis of chloride 5 7t-electrons take part in the rate-determining step

Nuclear Magnetic Resonance Spectroscopy. Analysis of the Proton Spectrum of Cyclobutene

A complete analysis of the proton n.m.r. spectrum of cyclobutene (I) has been made which shows that the couplings between the allylic and vinylic protons, while small, are by no means negligible; J_(13) = -0.80 C.P.S. and J_(15) = + 1.55 C.P.S. The analysis which involved ^(13)C satellite spectra of ordinary and specifically deuterated cyclobutene gave spin coupling and chemical shift parameters which predict that cyclobutene should show just two quite sharp peaks in its high-resolution n.m.r. spectrum in agreement with experiment

Solvolytic Behaviour of a Primary Squalene Derivative

Compounds 5 (4,8,13,17,21-pentamethyl-4,8,12,16,20-docasapen- taenyl chloride and tosylate) were prepared starting from squalene and the solvolysis rates were measured in 80% (v/v) aqueous ethanol. a-Deuterium secondary kinetic isotope effects and activation parameters were calculated, and the products were determined. According to the values obtained (/CH/JCD — 0.99 ± 0.06, A H={= = 86.6 kJ mol1, A S+ = —69.3 J mol-1 K-1) and on the basis of isolated aliphatic products (11 and 14) it is concluded that the substrate follows the SN2 type displacement reaction with solvent without jt^participation of the double bond

A kinetic approach to the mechanism of cationic polyolefinic cyclization. Simple and extended π-participation

This review deals with the mechanism of the biomimetic olefinic cationic polycyclizations considering relative rate effects, activation parameters, substituent rate effects, a, p correlation and secondary deuterium kinetic isotope effects (KIE) in solvolysis, obtained with tertiary and benzylic substrates comprising one, two or more double bonds, respectively, sited at the same positions as in the natural precursor (C-5, C-9, C-13). Kinetic behaviour of substrates with one double bond at position 5 (models for mono- cyclization) which are structurally related to structures 16U and 22U suggests that the formation of the first cyclohexane ring is a concerted process with some exceptions (16U with p-OCH3). In solvolysis of chlorides with double bonds at positions 5 and 9 (28 and 29U) extended it-parcipation occurs, i.e. both double bonds of the aliphatic chain are involved in the rate determining step. Substrastes with more then two double bonds (30U and 31U) solvolyze by way of extended 7i-participation. It remains unclear if two or three double bonds are involved. The paper also shows clear evidence that the magnitude of 3-deuterium secondary KIE are the most sensitive probe for neighboring group participation

Solvolysis rate of 3-methyl-2- (3-pentynyl) · 2-cyclohexenyl p-nitrobenzoate. A model system for n-participation of the CC triple bond

The synthesis of 3-methyl-2-:(3-rpentynyl)-2-cycloheocenyl p-nitro1benzoa1te is desc["ibed. This ester so1lvolyzes in 97°/o CF3CH20H at 2'5 °C without n-participa:tion of the CC trLple bond, showing solvoiysis rate retardaition in comparison with the saturated anafog. This result is e~piained by electron-withdrawing inductiove e1ffect 01f 1the CC trirple bond. The lo.g k va~ues of alkanyl- (4), alikenyl- (5, 6), and alkyny:l-substitJu·ted (10) esters show good linear correia1tion With the pK. values of the cOirresrponding car:boxyJ'ic acids

Solvolysis kinetics of 1-chloro-1-phenyl-5,9,14,18,22-pentamethyl-5,9,13,17,21-tricosapentaene, a squalene derivative. indication of participation

The title compound 1 was prepared starting from squalene and the solvolysis rates were measured in 80% (v/v) aqueous ethanol. The relative solvolysis rate and activation parameters were calculated. According to the values obtained it is concluded that 1 solvolyzes probably with participation of at least one double bond

Extended π-participation in biomimetic cyclization of squalene derivatives

Chlorides 4 (1-aryl-1-chloro-5,9,14,18,22-pentamethyl-5,9,13,17,21- tricosapentaenes) with various phenyl substituents were prepared, and solvolysis rates were measured in aqueous ethanol Op = 95% and 80%) and in aqueous 2,2,2-trifluoroethanol (w = 97%). Hammett p+ values obtained are -1.86, —1.81 and —1.56, respectively, suggesting concerted cyclization of at least two double bonds in the rate determining step