Conformational memory in enantioselective radical reductions and a new radical clock reaction

Citation
Aj. Buckmelter et al., Conformational memory in enantioselective radical reductions and a new radical clock reaction, J AM CHEM S, 122(39), 2000, pp. 9386-9390
Citations number
38
Categorie Soggetti
Chemistry & Analysis",Chemistry
Journal title
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
ISSN journal
00027863 → ACNP
Volume
122
Issue
39
Year of publication
2000
Pages
9386 - 9390
Database
ISI
SICI code
0002-7863(20001004)122:39<9386:CMIERR>2.0.ZU;2-T
Abstract
The radical decarboxylation of acid 1 led to tetrahydropyran 3 with signifi cant optical activity. This transfer of chirality is an example of a confor mational memory effect and derives from the slow ring inversion of the atro pisomer 2 and its enantiomer 2'. A similar conformational memory effect was observed in the reductive decyanation and reductive lithiation of cyanohyd rin 4. We propose that the racemization of radicals with chiral conformatio ns such as 2 could be used as new radical clocks. The rate of racemization of 2 was evaluated and used to determine the rate of H atom transfer to 2 b y different H atom donors. The rate of racemization of 2 is 5.7 x 10(8) s(- 1) at 22 degrees C, which is about five times faster than ring opening of a cyclopropylmethyl radical.