Diastereoselective spiroannulation of phenolic substrates: advances towards the asymmetric formation of the manumycin m-C7N core skeleton.
The asymmetric syntheses of two new spirolactones prepared in optically pure form from L-3-nitrotyrosine are described. The key step, an oxidative spiroannulation, was carried out on the optically active phenols 11a and 11b and afforded the new spirolactones 5a and 5b in 85% and 83% yields, respectively, as mixtures (3:1 dr) of diastereomers. The major diastereomers from these mixtures could be isolated in optically pure form by trituration using acetone-hexanes as the solvent. Thus, the optically active spirolactones (+)-5a (+ 92.8 degrees, c=0.125 acetone) and (+)-5b (+112.0 degrees, c= 0.125 acetone) were obtained after four synthetic steps from L-3-nitrotyrosine in 41% and 43% yield, respectively.
Plourde
Guy L
GL
University of Northern British Columbia, Department of Chemistry, 3333 University Way, Prince George, British Columbia, Canada. plourde@unbc.ca
Spaetzel
Randy R
RR
Kwasnitza
Jolene S
JS
Scully
Thomas W
TW
D008956:Models, Chemical; D010636:Phenols / Q000737:chemistry*; D011090:Polyenes / Q000138:chemical synthesis* / Q000737:chemistry*; D053284:Polyunsaturated Alkamides / Q000138:chemical synthesis* / Q000737:chemistry*; D013237:Stereoisomerism
D010636:Phenols; D011090:Polyenes; D053284:Polyunsaturated Alkamides; C054474:manumycin