RING-OPENING OF (CYCLOBUTYLMETHYL)LITHIUM AND 3-TERT-BUTYL-1-BICYCLO[1.1.1]PENTYL)METHYL]LITHIUM

The ring-opening of (cyclobutylmethyl)lithium (1) to 4-pentenyllithium (2) has been investigated in a solvent system composed of isooctane-d ibutyl ether (3:2 by volume). The isomerization of 1 to 2, which is mu ch 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; Delta H-double dagger = 14.2 +/- 1.2 kcal/mol, Delta S-double dagger = -17.3 +/- 5 eu. The two-step is omerization of 3-tert-butyl-1-bicyclo[1.1.1]pentyl)methyl]lithium (5) to 4-tert-butyl-2-methylidene-4-pentenyllithium (7) via -tert-butyl-3- methylidenecyclobutyl)methyl]lithium (6) in pentane-diethyl ether invo lves a very rapid initial ring-opening of 5 to 6 (t(1/2) < 15 min at - 131 degrees C) followed by a slower isomerization of 6 to 7 (t(1/2) ap proximate to 24 min at -7.7 degrees C).