1.Iridium-mediated isomerization-cyclization of bicyclic Pauson-Khand derived allylic alcohols.
Kavanagh Y1, Chaney CM, Muldoon J, Evans P. J Org Chem. 2008 Nov 7;73(21):8601-4. doi: 10.1021/jo8017439. Epub 2008 Oct 8.
Treatment of 2-(toluene-4-sulfonyl)-2,3,4,4a,5,6-hexahydro-1H-pyrindin-6-ol 10, accessed from the diastereoselective Luche reduction of a Pauson-Khand derived bicylic cyclopentenone, with a catalytic amount of (1,5-cyclooctadiene)(pyridine)(tricyclohexylphosphine)iridium(I) hexafluorophosphate 1 (Crabtree's catalyst) under a hydrogen atmosphere resulted in the formation of 4-(toluene-4-sulfonyl)-2-oxa-4-azatricyclo[188.8.131.52(3,8)]decane 12 as a single diastereoisomer. This process is likely to proceed via an initial Ir(I)-mediated isomerization of the alkene to form an N-sulfonyl enamine 11, followed by cyclization. Evidence to support this came when, after short reaction periods, 11 was isolated, characterized spectroscopically, and on resubmission to the reaction conditions formed 12.