
TY  - JOUR
A1  - Beckwith, ALJ 
A1  - Easton, CJ 
A1  - Lawrence, T 
A1  - Serelis, AK 
T1  - Reactions of methyl-substituted Hex-5-enyl and Pent-4-enyl radicals
JF  - Australian Journal of Chemistry
JO  - Aust. J. Chem.
Y1  - 1983
VL  - 36
IS  - 3
SP  - 545
EP  - 556
KW  - 
UR  - https://doi.org/10.1071/CH9830545 
N2  - Relative and absolute kinetic data have been determined for ring closure of methyl-substituted hex-5-enyl radicals: 2-methyl- (10a), 3-methyl-(4a), 4-methyl-(5a), 2,2-dimethyl-(10c), 3,3-dimethyl-(4c) and 4,4-dimethyl-hex-5-enyl (5c) radicals, generated by interaction of tributylstannane with the corresponding bromides (1a)-(3a) and (1c)-(3c). Each radical undergoes regiospecific or highly regioselective 1,5-cyclization more rapidly than does the unsubstituted radical (4d). The rate enhancements, which arise mainly from lowering of the activation energy, can be rationalized in terms of the gem-dimethyl effect. 1,5-Ring closures of monosubstituted species are stereoselective: 2-methyl- and 4-methyl-hex-5-enyl radicals (10a) and (5a) give mainly trans products, whereas 3-methylhex-4- enyl radical gives mainly the cis. This behaviour reflects the effect of the substituent on the stabilities of cyclic transition complexes in chair-like conformations. Ring closure of 2,2-dimethylpent-4-enyl radical or of 3,3-dimethylpent-4-enyl radical (19) could not be detected. 
ER  -

