Photochemische Reaktionen. 90. Mitteilung. Die UV.‐Bestrahlung von (E)‐5‐Isopropyl‐6‐methyl‐5,6‐epoxy‐hept‐3‐en‐2‐on

Abstract

Hans Herloff Inhoffen zum 70. Geburtstag gewidmet (15.111.76) Photolysis of (E)-5-Isopropyl-6-methyl-5,6-epoxy-hept-3-en-2-on. -Summary. This paper continues the series of investigations of the photochemistry of d,P-unsaturated y, d-epoxyketones, by examinating the photochemical behaviour of the aliphatic vinylogous epoxy-ketone 1, the chromophore of which is structurally similar to that of y,&epoxy-(E),P-ionone (44).On n,n*-excitation (A = 254 nm) 1 isomerizes mainly to the enol-cther 2 and gives as minor products the isomeric dihydrofurane 3, the 1,5-diketones 4 and 5 and the 1,3-diketone 6. To a smaller extent, 1 also undergoes photofragmentation to the furane 7, the allenyl-ketone 8 and the cyclopropenyl-ketone 9. On n,n*-excitation (A > 347 nm) 1 yields the photoisomers 3, 4, 5 and in traces the hydroxyallenyl-ketone 14, but no fragmentation products. It is shown that on irradiation at A = 254 nm the 1,5-diketone 4 isomerizes to 5, 6 and 15 and photodecarbonylates to the B. y-unsaturated ketone 16.The isomers 3, 4 and 5, obtained both from n,n*-and n,n*-excitation, rcpresent products of cleavage of the C(y)-0-bond in 1. The enolether 2, on the other hand, formed only by 3z,x*-excitation, results from cleavage of the C(y)-C(6)-bond.Finally, the fragmentation products 7, 8 and 9, which could be detected only on n,n*-excitation, may arise from a common intermediate g t) h.

Thermal Reactions of Epoxyenones and Epoxydienes in the Ionone Series

“…Thus, thermolysis of 5,6-epoxy-5,6-dihydro-~-ionone (1) through an untreated quartz or Pyrex tube tilled with quartz-rings gave, in addition to compounds 13 and 14, the diketone 15. As 15 was the major product formed upon treatment of 1 with BF3.Et20 in benzene solution [7], it appeared that on thermolysis of 1, 15 was formed by an acid-catalyzed rearrangement on the glass surface. Therefore, the tube and packing were treated with aqueous ethylenediaminetetraacetate (edta) solution according to the method of Buldwin el a/.…”

“…Racemic Epoxyenone (+)-I a ) Thermolysis of (+)-1 (325 mg, 1.56 mmol) at 585" in a silylated tube (conversion 41 %) yielded a mixture of 13 (78%), 14 [25] (5%). and 15 [7] (2%), according to GC and 'H-NMR. Several batches were combined and chromatographed (AcOEt/hexane 1 :9) and the products finally purified by HPLC (AcOEt/hexane 1:33).…”

“…The diuinyl ether 17 was hydrolyzed (aq. CH3COOH) to the known diketone 62 [7] (Scheme 12). The enol-/J-diketone 36 was transformed to the cycloheptenone 63 by reaction with KOH (Scheme 12) (for analogous reactions of 2-acetyl-cycloalkanones, see [29]).…”

Ring Expansions of Vinyloxiranes, -thiiranes, and -aziridines: Synthetic Approaches, Challenges, and Catalytic Success Stories

“…Photochemical studies (Scheme b) have focused on a very specific class of vinyloxirane substrates containing a tetrasubstituted oxirane and a conjugated olefin. Eichenberger confirmed that such substrates could be ring expanded to afford 2,5-dihydrofuran products, albeit in very poor yield. Sakamoto verified that conjugated nitriles behaved differently than the enones reported by Eichenberger.…”