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

AbstractThe rates of photo‐oxidation of exocyclic S‐cis‐butadienes grafted onto bicyclo‐[2.2.1]heptanes and 7‐oxabicyclo[2.2.1]heptanes (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 (1), 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‐pe‐roxide 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 α, β‐unsaturated γ‐hydroxy aldehydes in the presence of catalytic amounts of Rh2(CO)4Cl2.