Mechanistic and Synthetic Studies on the Formation of 1,2,4-Trioxanes Related to Arteannuin. Photooxygenation of a bicyclic dihydropyran

✍ Scribed by Charles W. Jefford; Ying Wang; Gérald Bernardinelli

• Publisher: John Wiley and Sons
• Year: 1988
• Tongue: German
• Weight: 672 KB
• Volume: 71
• Category: Article
• ISSN: 0018-019X
• DOI: 10.1002/hlca.19880710822

✦ Synopsis

Dedicated to Dr. Edward C. Taylor on the occasion of his 65'h birthday (1 6.VIII. 88)

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%), (lR,4R,4aS,7R)-3,4,4a,5,6,7-hexahydro-4,7-dimethyl-lH-2-benzopyran-2-y1 hydroperoxide (19; 16.7 %), a 12 :1 ratio of (3R, 4aR, 7R, 7aS, IOR, 11 aR)-7,7a, 8,9,10,1l-hexahydro-3,7,10-trimethyl-6t1-[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 (Me,SiOTf) to the acetone solution of 16 after photooxygenation afforded (4aR,7R,7aS,lOR,l I aR)-7,7a,8,9,10,1l-hexahydro-3,3,7,1O-tetramethyl-6H-[2]benzopyrano[l,8a-e]-l,2,4-trioxane (23, 40%). The photooxygenation of 16 in CH,CIz at -78" followed by addition of acetone and Me,SiOTf afforded 17 (1 1 YO), 23 (59%), and (4aR,7R,7aS,lOR,l laR)-7,7a,8,9,10,1 I-hexahydro-3,3,7,10-tetramethyl-6H-[2]benzopyrano[8a,l-e]-1,2,4-trioxane (24; 5 "10). Repetition of the last experiment, but replacing acetone by cyclopentanone, gave 17 (16%), (4'aR,7'R.