The reaction of (2‐norborneno)[c]furan (4) with maleic anhydride gave 11‐oxa‐endo‐tetracyclo[6.2.1.13,6.02,7]dodec‐2(7)‐ene‐9,10‐exo‐dicarboxylic anhydride (5) and, with methyl acetylenedicarboxylate, methyl 11‐oxa‐endo‐tetracyclo [6.2.1.13,6.02,7]dodeca‐2(7),9‐diene‐9,10‐dicarboxylate (7). The syn‐11‐oxa‐sesquinorbornenes 5 and 7 could be equilibrated with their cycloaddents. They are at least 2 kcal/mol more stable than the corresponding anti‐sesquinorbornenes 6 and 8. The structure of 7 was deduced from its spectral data, by epoxidation with air or a peracid to give the exo‐epoxide 13 and by catalytic hydrogenation to give 14. The structure of 5 was established by single‐crystal X‐ray diffraction. A dihedral angle of 163° was measured between the C(1,2,7,8) and C(2,3,6,7) planes in 5. This important deviation from planarity for the C(2,7) double bond is attributed to (π, ω)‐repulsive interactions that make the π‐electron density of 2‐norbornene and 7‐oxa‐2‐norbornene derivatives preferentially polarized toward the exo‐face. This finding is discussed in relation with the relative stability of the syn‐ and anti‐ 11‐oxasesquinorbornenes and with the endo‐stereoselectivity of the cycloadditions of the norbornenofuran 4.
Azides are very versatile precursors of organic synthesis functionalities such as amines, isocyanates, sulfonamides, triazoles, tetrazoles, triazolines, aziridines, amino acids and diazo compounds. In industry, one of the favourite starting materials for these syntheses is sodium azide
which can generate hydrazoic acid whose toxicity and detonation potential is of major safety concern. However sodium azide is used daily in large tonnage in the air-bags of vehicles, in biologic institutes as a bactericide and in agriculture as a herbicide. In industrial synthesis, sodium
azide is actually the starting material of herbicides, anti-HIV pharmaceuticals, anti-pain compounds and hypo tensors. This massive use of sodium azide represents severe toxicological and physical damage risks. The industrial synthesis under the scope of this presentation will be the manufacture
of a tetrazole produced in several tens of tons per year. A risk assessment concluded that it would be necessary to conduct the reaction in a 'Bunker' and to minimise risks by absolutely avoiding generation of hydrazoic acid. This can be achieved by a careful design of the process and by strict
organisational measures. Furthermore, the reaction equipment was designed to prevent any condensation of hydrazoic acid. One way to prevent its formation is to maintain the reaction medium under basic conditions at all times. This is achieved by using triethylamine hydrochloride as a buffer.
In the applied reaction conditions it could be demonstrated that triethylamine was the refluxing compound at 130 °C and that a thermally stable triethyl ammonium azide was formed. The environmental problem could be resolved by incineration of the wastewaters. In conclusion, reactions with
sodium azide are safe, they only need a stabilising agent. A search for such compounds could be an interesting but rather dangerous research project.
SummaryPalladium-catalyzed double carbomethoxylation of the Diels-Alder adduct of furan and maleic anhydride yielded the methyl all-exo-7-oxanorbornane-2,3,5,6-tetracarboxylate (7) which was transformed in three steps into 2,3,5,6-tetramethylidene-7-oxanorbornane (l), a useful synthon. Six isomeric methyl 7-oxanorbornane-2,3,5,6-tetracarboxylates (7-12) have been isolated and their 'H-and 13C-NMR. data are compared.
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.
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