syn-Sesquinorbornatriene, possibly the extreme example of x-bond pyramidalization, has been synthesized and characterized. Cycloaddition of (Z)-1,2-bis(phenylsulfonyl)ethylene with tricyclo[5.2.1 .02-6]deca-2,5,8-triene proceeds with at least 95% below-plane stereoselectivity to give the syn [4 + 21 adduct. Mild reductive desulfonylation of this product leads to the above hydrocarbon. Its I3C NMR shifts are particularly instructive when compared to syn-sesquinorbornadiene, which was prepared in comparable fashion. Peracid oxidation of the original adduct, followed by comparable treatment with I-2% sodium amalgam, affords the structurally related diene epoxide. Sequential photocyclization and periodic acid cleavage of this intermediate delivers [4]peristylane-2,4-dione and constitutes an expedient route to this hemispherical compound. By comparison, the Diels-Alder reaction of tricyclo[5.2.1 .@6]deca-2,5,8-triene with (E)- 1,2-bis(phenylsulfonyl)ethylene is sterically controlled and proceeds with predominant above-plane dienophile capture. Reductive desulfonylation of this adduct affords anti-sesquinorbornatriene. Although this hydrocarbon is sensitive to air oxidation, it is somewhat less so than its syn counterpart. Nonetheless, the 13C chemical shift of its internal olefinic carbon (173.23 ppm) appears slightly to lower field than that of the syn isomer (172.14 ppm). The possible contributory causes to the extreme deshielding of these signals are discussed in light of comparison with lesser unsaturated congeners and orbital interaction patterns. Finally, heating tricyclo[5.2.1 .0296]- deca-2,5,8-triene with the (E)-disulfone in toluene leads efficiently to an angular above-plane adduct. Removal of the sulfonyl groups in this instance give s rise to a structural isomer of the above pair of trienes that does not share their high reactivity toward triplet oxygen
Consequences of Fixing 3 Parallel Coplanar Double-bonds In Close Proximity With Different Geometries - Synthesis and Spectral Parameters of Syn-sesquinorbornatriene and Anti-sesquinorbornatriene
LICINI, GIULIA MARINA;
1986
Abstract
syn-Sesquinorbornatriene, possibly the extreme example of x-bond pyramidalization, has been synthesized and characterized. Cycloaddition of (Z)-1,2-bis(phenylsulfonyl)ethylene with tricyclo[5.2.1 .02-6]deca-2,5,8-triene proceeds with at least 95% below-plane stereoselectivity to give the syn [4 + 21 adduct. Mild reductive desulfonylation of this product leads to the above hydrocarbon. Its I3C NMR shifts are particularly instructive when compared to syn-sesquinorbornadiene, which was prepared in comparable fashion. Peracid oxidation of the original adduct, followed by comparable treatment with I-2% sodium amalgam, affords the structurally related diene epoxide. Sequential photocyclization and periodic acid cleavage of this intermediate delivers [4]peristylane-2,4-dione and constitutes an expedient route to this hemispherical compound. By comparison, the Diels-Alder reaction of tricyclo[5.2.1 .@6]deca-2,5,8-triene with (E)- 1,2-bis(phenylsulfonyl)ethylene is sterically controlled and proceeds with predominant above-plane dienophile capture. Reductive desulfonylation of this adduct affords anti-sesquinorbornatriene. Although this hydrocarbon is sensitive to air oxidation, it is somewhat less so than its syn counterpart. Nonetheless, the 13C chemical shift of its internal olefinic carbon (173.23 ppm) appears slightly to lower field than that of the syn isomer (172.14 ppm). The possible contributory causes to the extreme deshielding of these signals are discussed in light of comparison with lesser unsaturated congeners and orbital interaction patterns. Finally, heating tricyclo[5.2.1 .0296]- deca-2,5,8-triene with the (E)-disulfone in toluene leads efficiently to an angular above-plane adduct. Removal of the sulfonyl groups in this instance give s rise to a structural isomer of the above pair of trienes that does not share their high reactivity toward triplet oxygen
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