REACTION OF ALLYL SULFONES WITH 1-BROMOTRICYCLO[4.1.0.02,7]HEPTANE

Vasin Viktor Alekseevich, Doctor of chemical sciences, professor, head of sub-department of organic chemistry, Ogarev Mordovia State University (68 Bolshevistskaya street, Saransk, Russia), vasin@mrsu.ru
Korovin Dmitry Yurevich, Engineer, Ogarev Mordovia State University (68 Bolshevistskaya street, Saransk, Russia), orgchem@mrsu.ru

547.598 : 544.433.3

Background. Functionally substituted bicyclo[3.1.1]heptanes (norpinanes) are synthetic analogues of biologically active natural terpenes of pinane series. So far, these compounds have been relatively poorly studied. However, many of them are efficient building blocks in multi-step synthesis of complex polycyclic structures containing small-sized carbocycles. They are convenient models both for the special physical chemistry research and for the study of the spatial structure and conformational features of molecules with a core containing fused cyclohexane rings in position 1 and 3. In addition, it is known that the compounds exhibit a variety of biological activities. Therefore, the development of simple methods for directing the synthesis of functionally substituted bicyclo[3.1.1]heptanes and the study of their chemical properties are urgent tasks that can greatly expand the range of norpinane compounds and the derived products. Our recent research in this area shows that an effective approach for the synthesis of norpinane compounds is the bicyclobutane strategy. It is based on the selective cleavage of the central C–C bond in a relatively complex, but generally more available than norpinanes, namely, bicyclo[1.1.0]butane derivatives – tricyclo[4.1.0.02,7]heptanes. Free-radical sulfonation reactions of tricycloheptane with halogenanhydrides, thio- and selenoesters, azides, cyanides and thiocyanates of sulfoacides and, as we have recently shown, (phenyl)ethynyl- and allyl sulfones are highly prospective for the synthesis of sulfonyl-substituted norpinanes. Electron-withdrawing sulfonyl group strongly stabilizes α-carbanions generated by base treatment. It provides additional opportunities of chemical modification of norpinanes by formation of novel C–C bonds and carbon cores of organic compounds via participation of the carbanions. Note that, if necessary, sulfonyl group can be removed by elimination or replacement reactions.
Materials and methods. 1-Bromotricyclo[4.1.0.02,7]heptane, allyl(phenyl)- and allyl(methyl) sulfones containing electron-withdrawing substituent at vinyl atom С2 are used for the synthesis of novel norpinanes. The reactions of equimolar quantities of these compounds were carried out in refluxing dry toluene under argon atmosphere in the presence of benzoyl peroxide as a radical initiator for 22 – 32 h. Composition of the products is controlled by thin layer chromatography and NMR 1Н and 13С.
Results. In each case, norpinane monoadduct was obtained as a major product. It corresponds to endo, anti-selective addition of allyl sulfone at the central С1–С7 bond of tricycloheptane with breakage of allyl carbon – sulfur bond. The products were isolated in individually by dry-column flash chromatography on silica gel and crystallization in the yields of 28–45 %. Their structure was determined by the elemental analysis and spectral methods (IR, one- and two-dimension NMR). The phenyl (2-N-phenylcarbamoylallyl) sulfone adduct was treated by double excess of potassium tert-butoxide in THF at 0 °С. It led to a 1,3-elimination of hydrogen bromide and reconstitution of the tricyclo[4.1.0.02,7]heptane system. At the experimental conditions, 1,7-disubstieted tricycloheptane is unstable and undergoes strong base-catalyzed isomerization to diene derivative – N-phenyl-2-[6-exo-(phenylsulfonyl) bicyclo[3.1.1]hept-7-ylidenmethyl]acrylamide.
Conclusions. Radical initiated cascade reactions of 1-bromotricyclo[4.1.0.02,7]heptane with allyl sufones, containing additional electron-withdrawing substituent in position 2, can be used for highly regio- and stereoselective synthesis of novel bicyclo[3.1.1]heptanes (norpinanes). They are of interest as convenient precursors of frame and bridged systems with a complex structure. In particular, under strong base conditions, these compounds can be transformed into conjugated dienes with norpinane core.

allyl sulfone, radical addition, tricyclo[4.1.0.02,7]heptane, bicycle[3.1.1]heptane, norpinane, dehydrobromination, ethynyl sulfone.

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