ISSN:
0018-019X
Keywords:
Chemistry
;
Organic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The photooxygenation of (4R,4aS,7R)-4,4a,5,6,7,8-hexahydro-4,7-dimethyl-3H-2-benzopyran (16) was performed in (i) MeOH, (ii) acetaldehyde, and (iii) acetone at -78°. The products obtained respectively were (i) (2R)-2-[(1S,4R)-4-methyl-2-oxocyclohexyl]propyl formate (17; 72% yield), (ii) 17 (54.5%), (1R,4R,4aS,7R)-3,4,4a,5,6,7-hexahydro-4,7-dimethyl-1H-2-benzopyran-2-yl hydroperoxide (19; 16.7%), a 12:1 ratio of (3R,4aR,7R,7aS,10R,11aR)-7,7a,8,9,10,11-hexahydro-3,7,10-trimethyl-6H-[2]benzopyrano[1,8a-e]-1,2,4-trioxane (20) and its C(3)-epimer 21 (17%), together with evidence for the 1,2-dioxetane (22) originating from the addition of dioxygen to the re-re face of the double bond of 16, and iii) unidentified products and traces of 22. Addition of trimethylsilyl trifluoromethanesulfonate (Me3SiOTf) to the acetone solution of 16 after photooxygenation afforded (4aR,7R,7aS,10R,11aR)-7,7a,8,9,10,11-hexahydro-3,3,7,10-tetramethyl-6H-[2]benzopyrano[1,8a-e]-1,2,4,-trioxane (23, 40%). The photooxygenation of 16 in CH2Cl2 at -78° followed by addition of acetone and Me3SiOTf afforded 17 (11%), 23 (59%), and (4aR,7R,7aS,10R,11aR)-7,7a,8,9,10,11-hexahydro-3,3,7,10-tetramethyl-6H-[2]benzopyrano[8a,1-e]-1,2,4-trioxane (24; 5%. Repetition of the last experiment, but replacing acetone by cyclopentanone, gave 17 (16%), (4′aR,7′R,7′aS,10′R,11′aR)-7′,7′a,8′,9′,10′,11′-hexahydro-7′,10′-dimethylspiro[cyclopentane-1,3′-6′H-[2]benzopyrano[1,8a-e]-1,2,4-trixane] (25; 61%), and (4′aR,7′R,7′aS,10′R,11′aR)-7′,7′a,8′,9′,10′,11′-hexahydro-7′,10′-dimethylspiro[cyclopentane-1,3′-6′H-[2]benzopyrano[8a,1-e]-1,2,4-trixane] (26, 4%). The X-ray analysis of 23 was performed, which together with the NMR data, established the structure of the trioxanes 20, 21, 24, 25, and 26. Mechanistic and synthesis aspects of these reactions were discussed in relation to the construction of the 1,2,4-trioxane ring in arteannuin and similar molecules.
Additional Material:
1 Tab.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/hlca.19880710822
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