Effects of Remote Substitution on the Photo‐oxidation of Exocyclic s‐cis‐Butadienes Grafted onto Bicyclo [2.2.1]heptanes. Thermal and Rhodium Catalyzed Rearrangements of 3,6‐Dihydro‐1,2‐dioxines

Abstract

SummaryThe rates of photo-oxidation of exocyclic s-cis-butadienes grafted onto bicyclo-[2.2. llheptanes and 7-oxabicyclo[2.2. llheptanes (1-6) are dependent upon remote modifications of the bicyclic skeletons. They correlate with the rates of Diels-Alder additions of these dienes to strong dienophiles. The 2,3-dimethylidenenorbornane (l), 5,6-dimethylidene-2-norbornene (2) and 2,3-dimethylidene-7-oxanorbornane (3) gave the corresponding endo-peroxides (3,6-dihydro-1,2-dioxines) 7-9 in good yield. The 2,3,5,6-tetramethylidene-7-oxanorbornane (4) gave the mono-endo-peroxide 6, the latter did not react with a second equivalent of oxygen. Similarly, 5,6-dimethylidene-7-oxa-2-norbornene (5) was unreactive toward photo-oxidation. Thermal isomerization of the endo-peroxides 7 and 9 gave the trans-diepoxides 10 and 14, respectively, with high stereoselectivity. The endo-peroxides 6 , 7 and 9 were cleanly isomerized into the corresponding a. /?-unsaturated y-hydroxy aldehydes in the presence of catalytic amounts of Rh, (CO)&l2.

Conformational Analysis of Endoperoxides Grafted onto Bicyclo[2.2.n]alkanes as a Test of the Rigidity of the Bicyclic Skeleton. Photo‐oxidation of [2.2.2] Hericene and 2,3,5,6‐Tetramethylidenebicyclo[2.2.n]alkanes

“…The mono-endoperoxide 13 has already been reported [9]. It was then found that the photo-oxidation of 13 into the his-endoperoxide 18 was a very slow process.…”

“…By monitoring the reaction using 360-MHz 'H-NMR (without concentrating the irradiated solutions), we were able to observe 18, a coinpound which decomposed rapidly at -20" on concentration of the solution. The photo-oxidation of triene 23, an analog of 8, was also found to be an extremely slow process [9]. Again, using high-field 'H-NMR to monitor the reaction, the corresponding endoperoxide 24 could be observed at -20".…”

“…Weak bases or acids are capable of promoting the rearrangement 19+22 [9]. The aromaticity of 20 provides the driving force for the cycloreversion.…”

“…No evidence was obtained for the corresponding endoperoxides to act as physical quenchers of '0,. In the presence of DABCO (1,4-diazabicyclo-[2.2.2]octane), the photo-oxidations were retarded [9]. Moreover, when '0, was generated by thermal decomposition of the endoperoxide derived from 9,lO-diphenylanthracene …”

“…Polyenes 6 8 and 23 were found to be poor physical quenchers of the photo-oxidation of cyclopentadiene (see e.g. [9] [ l l ] [19]). No evidence was obtained for the corresponding endoperoxides to act as physical quenchers of '0,.…”