ISSN:
0894-3230
Keywords:
Organic Chemistry
;
Physical Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
The cycloaddition reactions of 4-methylphenylthio-, methoxy-, 4-methoxyphenyl-, phenyl-, chloro- and cyanoallene with tert-butylthioacrylonitrile (BTA) in toluene-d8 solution were investigated. The relative reactivity sequence of these substituted allenes is 4-methylphenylthio ∼ methoxy- 〉 4-methoxyphenyl- 〉 phenyl- 〉 chloro- 〉 cyanoallene. Activation parameters were measured for diradical intermediate formation of BTA with 4-methylphenylthio-, methoxy- and 4-methoxyphenylallene, giving average values of Ea and ΔS± of 14.2-16.8 kcal mol-1 and ca. -33 eu, respectively. The relative reactivity sequence is consistent with a FMO allene-HOMO, BTA-LUMO dominant interaction for diradical intermediate formation. However, the regioselectivity of attack on the substituted allene appears to be thermodynamically controlled. The formation of the diradical intermediates in these cycloaddition processes appears to be irreversible. However, the ring closure of the diradical intermediates formed from 4-methylphenylthio-, methoxy- and 4-methoxyphenylallene is reversible under the conditions of the kinetic experiments. The kinetically controlled ring closure of the diradical intermediates is allyl radical SOMO controlled, while the final cycloadduct distribution is thermodynamically controlled.
Additional Material:
1 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/poc.610050308
Permalink
