The order of reactivity towards SH2 attack by tributyltin radicals on various groups X in four different molecular environments (RCO2CH2X, RCH2OCH2X, XCH2CO2Et and RCH2X) has been found by competition experiments to be Br > PhSe > Cl > p-CNC6H4S > PhS > p-MeC6H4S > MeS . The mechanism of the reaction of chloromethyl phenyl sulfide with alkoxides is discussed.
Multipath couplings involving 1H-1H, and
13C-13C nuclei in a variety of 1-substituted bicycloalkanes are treated according to additivity principles based on empirical coupling increments derived from model hydrocarbons. The coupling constants are essentially additive in practically all series except for derivatives of bicyclo [1.1.1]pentane; non-additivities of several couplings in the latter are ascribed to the effects of contributions arising from through-space bridgehead-bridgehead interactions, as well as from mutual electronic perturbations between the different pathways. The results are compared with those derived previously from theoretical calculations, which also have some difficulty in reproducing the experimental data in the case of the bicyclo [1.1.1] pentyl system.
Ring opening of the (bicyclo[1.1.1]pent-1-yl)methyl (4), (bicyclo[2.1.1]hex-1-yl)methyl (5) and (bicyclo[3.1.1]hept-1-yl)methyl (6) radicals has been investigated by semiempirical molecular orbital theory MINDO/3 and AM1) and by experiment. Our results indicate that (4) ring-opens extremely rapidly, with an estimated energy barrier of less than 22 kJ mol-1. The higher homologues (5) and (6) rearrange more slowly with barriers of about 42.2 and 46.0 kJ mol-1 respectively. This trend is also observed in the MINDO/3 and AM1 results, with the latter giving the better agreement with experiment.
Ring expansion of several
1-substituted bicyclo[2.1.1]hexan-2-ones has been investigated in order to
compare the effect of substitution on the migratory aptitude of the bridgehead
carbon in relation to the methylene carbon. In the cases examined it was observed
that there is a marked preference for migration of the methylene carbon, with
the substituted substrates displaying higher regioselectivity
than the parent ketone. In the rearrangement of both 1-fluoro- and
1-chloro-bicyclo[2.1.1]- hexan-2-one, migration of the methylene carbon occurs
exclusively.
The attempted conversion of tricyclo [3.1.1.03,6]heptane-6-methanol (9) into the corresponding tosylate (7) leads instead to a rearranged isomer tricyclo [3.2.1.03,6]oct-6-yl tosylate (10). Treatment of 10 with lithium aluminium hydride affords a mixture of the parent alcohol tricyclo[3.2.1.03,6]octan-6-ol (15) and endo-bicyclo[3.2.l]octan-6-ol. The available evidence suggests that the latter arises by a process which appears to be mediated by alkoxy radicals rather than anions.
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