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.

The syntheses of 2,3-dimethylidene-and 2,3,5,6-tetramethylidene-7-oxabicyclo[2.2. llheptanes substituted in position C(1) are reported. The 1-dimethoxymethyl group in derivatives 2 and 6 controls the regioselectivity of the Lewis-acid-catalyzed Diels-Alder additions with methyl vinyl kctone and butynone. For the EtAIC1,-catalyzed addition of methyl vinyl ketone to 6, the regioselectivity can be reversed by a small solvent modification. The tetraene 2 is a versatile reagent for regioselective 'tandem' cycloadditions.

The I-dimethoxymethyl-5,6-dimethylidene-7-oxabicyclo[2.2. I jhept-2-ene (9) has been prepared. On treatment with Fe,(CO),, the endocyclic double bond C(2)=C (3) . Oxidative removal of the Fe(CO)T moiety in 13 and 14 did not afford the expected ortho-quinodimethane derivatives but led to CO insertions giving 2,3-dihydro-2-0x0-1 H-indene-4-carbaldehyde (20) and methyl 7-formyI-2,3-dihydro-2-0~0-1 H-indene-5-carboxylate (21), respectively.

Die Titelverbindung (V) wird auf dem beschriebenen Weg synthetisiert und einer Reihe von Diels‐Alder‐Reaktionen mit den Verbindungen (VI), (IX) und (XI) unterworfen.