Transformation of a-Dihydroionol to Dihydroedulan and Theaspyrane by Photosensitized Oxygenation
Year: 1979
Type: article
Abstract: Racemic dihydroedulan (1) and theaspyrane (2) have -been synthesized starting with racemic a-dihydroionol (2) in a few steps using photosensitized oxygenation as the key step.Two isomeric hydroxy allyl alcohols 4 and 5 were obtained upon treatment with singlet oxygen and also prepared from an epoxide Z by treatment with lithium diethylamide and organoselenium reagents, respectively.The allyl alcohol 5 afforded dihydroedulan (A) predominantly with BF3 in THF and another allyl alcohol 4 was converted selectively to theaspyrane (2) through a diene 9 .-Dihydroedulan and theaspyrane ( 2 ) are components responsible for the unique flavor of the juice of the purple-skinned passionfruit PassifloraSimsl and black tea aromas2 respectively, and they were obtained as an epimeric mixture isolated in a trace amount from nature.Therefore, it is very interesting and even important to approach such valuable flavors synthetically from a starting material readily available.Recently, multistep synthesis of 1 was achieved starting with -1 3-(4-oxo-2,2,6-trimethylcyclohex-5-enyl)propanenitrile or a-iononeP3 and synthetic studies on theaspyrane derivatives were extensively carried out.4,5'6However, a more efficient and practical route to these unique flavors was desired urgently.We report here a new, simple, and obviously more practical synthesis of an epimeric mixture of dihydroedulan and theaspyrane from the same starting material by photosensitized oxygenation.
Source: Heterocycles
Authors: Masaji Ohno, Hideki Okawara, Susumu Kobayashi
Institution: The University of Tokyo
Language: English
Subfield: Organic Chemistry
Field: Chemistry
Domain: Physical Sciences
Open Access status: diamond
OpenAlex ID: W4229681650