Ring-Opening of (Cyclobutylmethyl)lithium and pentyl)methyl>lithium

Article abstract of DOI:10.1021/jo00107a005

The ring-opening of (cyclobutylmethyl)lithium (1) to 4-pentenyllithium (2) has been investigated in a solvent system composed of isooctane-dibutyl ether (3:2 by volume).The isomerization of 1 to 2, which is much more rapid than is cleavage of the corresponding Grignard reagent, is characterized by the following activation parameters: E_a = 14.7+/-1.2 kcal/mol, ln A = 21.6+/-2.5; ΔH(excit.) = 14.2+/-1.2 kcal/mol, ΔS(excit.) = -17.3+/-5 eu.The two-step isomerization of <(3-tert-butyl-1-bicyclo<1.1.1>pentyl)methyl>lithium (5) to 4-tert-butyl-2-methylidene-4-pentenyllithium (7) via <(1-tert-butyl-3-methylidenecyclobutyl)methyl>lithium (6) in pentane-diethyl ether involves a very rapid initial ring-opening of 5 to 6 (t_1/2 < 15 min at -131 deg C) followed by a slower isomerization of 6 to 7 (t_1/2 ca. 24 min at -7.7 deg C).