Direct Oxa-Pictet−Spengler Cyclization to the Natural (3a,5)-trans-Stereochemistry in the Syntheses of (+)-7-Deoxyfrenolicin B and (+)-7-Deoxykalafungin
JOURNAL OF ORGANIC CHEMISTRY(2009)
摘要
The pyranonaphthoquinones (+)-7-deoxyfrenolicin B and (+)-7-deoxykalafungin were synthesized in four steps using an oxa-Pictet-Spengler cyclization that directly provided the natural (3a,5)-trans-substituted dihydronaphthopyrans with high diastereoselectivity. This outcome is in contrast to the unnatural (3a,5)-cis-substituted dihydronaphthopyrans reported under similar conditions for the syntheses of (+)frenolicin B and (+)-kalafungin. Computational modeling is presented that provides insight into this unusual stereoselectivity.
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关键词
syntheses,oxa-pictet
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