Prins Cyclizations: Labeling Studies and Application to Natural Product Synthesis
摘要:
[GRAPHICS]The first syntheses of two natural products, catechols 1 and 2, isolated from Plectranthus sylvestris (labiatae), are reported. Oxygen-18 labeling studies support the proposed intermediacy of a stabilized benzylic cation in the acid-promoted cyclization of an aldehyde and benzylic homoallylic alcohol possessing an electron-rich aromatic ring, In contrast, with an electron-deficient aromatic ring the pathway via a benzylic cation is only minor.
Metal-Free Brønsted Acid-Catalyzed Rearrangement of δ-Hydroxyalkynones to 2,3-Dihydro-4<i>H</i>-pyran-4-ones: Total Synthesis of Obolactone and a Catechol Pyran Isolated from <i>Plectranthus sylvestris</i>
作者:Sachin P. Gholap、Dashrath Jangid、Rodney A. Fernandes
DOI:10.1021/acs.joc.8b03141
日期:2019.3.15
A metal-free, Brønsted acid, pTsOH-catalyzed intramolecular rearrangement of δ-hydroxyalkynones to substituted 2,3-dihydro-4H-pyran-4-ones was developed. The rearrangement occurs with high regioselectivity under mild and open-air conditions. The scope of work was illustrated by synthesizing an array of aliphatic and aromatic substituted 2,3-dihydro-4H-pyran-4-ones in up to 96% yield, 100% atom economy