ISSN:
0018-019X
Keywords:
Chemistry
;
Organic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
Synthesis of the Lichen Macrolide (+)-Aspicilin Using Photolactonization as a Key Reaction(+)-Aspicilin, obtained from a lichen source of the Black Forest, has been proven to have the absolute configuration depicted by formula la. It is easily built up from phenol (14a), 1,9-nonanediol (13a), and (-)-(S-) methyloxiarane (6) (cf. Scheme 2). The latter building block provides the first stereogenic center C(17). The heterocycle is produced by photolactonization, fairly early during the course of the synthesis. The second stereogenic center is generated diastereoselectively at C(6) in compound 8, conveniently available from photolactone 9a or 9b/9c. Its absolute configuration depends on the kind of reducing agent and is controlled by long-range conformational transmission of chiral information. To explore the cause of stereoselection, 2D-NMR spectroscopy, X-ray structural analysis, and/or computer-aided conformational search followed by energy minimization have been used extensively, revealing the importance of the local conformation of the lactone moiety. Compound 8, on treatment with Yamamoto's reagent, affords pre-target compound 7a almost exclusively. The latter compound, on pyridine-accelerated dihydroxylation with OsO4, gives preferentially (+)-Aspicilin.
Additional Material:
37 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/hlca.19880710719
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