The effect of non-bonded interactions on the regioselectivity of cyclization of the hex-5-enyl radical
- 1 January 1979
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in Journal of the Chemical Society, Perkin Transactions 2
- No. 11,p. 1535-1539
- https://doi.org/10.1039/p29790001535
Abstract
Treatment of 1-bromo-2,2,5-trimethylhex-5-ene (9a) with tributylstannane affords 2,5,5-trimethylhex-1-ene (13a), 1,1,3,3-tetramethylcyclopentane (12a), and 1,1,4-trimethylcyclohexane (15a). Accurate determination of the yields allows the rate constants for the endo- and exo-modes of cyclization of the 2,2,5-trimethylhex-5-enyl radical (10a) to be determined. Comparison of the kinetic parameters with those for the 2,2-dimethylhex-5-enyl radical (10b) and related species indicates that interaction of the pseudo-axial 2-methyl substituent with the syn-proton at C-6 disfavours the formation from (10b) of the chair-like six-membered transition state (5). The effect is, however, too small to account for the high regioselectivity of ring closure of the parent hex-5-enyl radical.Keywords
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