β-Silyl Arenes in the Arene-Olefin Photocyclization Reaction

Abstract

The ‘β-silyl effect’ of ground-state chemistry has been found to be operative in excited-state systems as well, where it exerts just as remarkable of an effect on the yields and selectivity of the intermolecular arene-olefin photocyclization reaction. Benzyl­trimethylsilane has been found to undergo intermolecular arene-olefin photocyclization with alicyclic hydrocarbon alkenes to provide 2,6-meta-adducts with yields of 65-90% in a regio- and stereo­selective manner. Particularly encouraging are the reactions with cyclohexene and with cis-cyclooctene, as both of these substrates give anomalous results with many arenes, but fall perfectly in line when coupling with benzyltrimethylsilane. These data augur well for the use of β-silyl directing groups in more complex photocyclization reactions. The ability of a C-Si sp³ bond to stabilize an incipient positive charge in the β-position by hyperconjugation apparently also allows it to stabilize a transiently electron-deficient excited state, in the same way that an electron-donating group (e.g., a methyl or a methoxy group) has been observed to direct the regiochemistry of the arene-olefin photocyclization reaction. To fully characterize the photoadducts, they have been elaborated via radical addition of substituted thiophenols to crystalline compounds and X-ray crystal structures obtained.

Key words

photochemistry - cycloadditions - neighboring group effects - hyperconjugations - radical reactions

References

• 1 Bryce-Smith D. Drew MGB. Fenton GA. Gilbert A. Proctor A. J. Chem. Soc., Perkin Trans. 2  1991,  779 
• For reviews see:
• 2a Cornelisse J. Chem. Rev.  1993,  615 
• 2b Wender PA. Siggel L. Nuss JM. Org. Photochem.  1989,  10:  357 
• 3 Ors JA. Srinivasan R. J. Org. Chem.  1977,  42:  1321 
• 4 Bryce-Smith D. Foulger B. Forrester J. Gilbert A. Orger BH. Tyrell HH. J. Chem. Soc., Perkin Trans. 1  1980,  55 
• 5 Sheridan RS. Tetrahedron Lett.  1982,  23:  267 
• 6 Bryce-Smith D. Fenton GA. Gilbert A. Tetrahedron Lett.  1982,  23:  2697 
• 7 Baciocchi E. Crescenzi M. DelGiacco T. J. Chem. Soc., Perkin Trans. 1  1991,  3377 
• 8 Baciocchi E. J. Chem. Soc., Chem. Commun.  1992,  59 
• 9 Wender PA. Dore TM. deLong MA. Tetrahedron Lett.  1996,  37:  7687 
• 10 Gilbert A. Yianni P. Tetrahedron Lett.  1977,  18:  242 
• 11 Reedich DE. Sheridan RS. J. Am. Chem. Soc.  1985,  107:  3360 
• 12 Yamamura S. Shizuri Y. Shigemori H. Okuno Y. Ohkubo M. Tetrahedron  1991,  47:  635 
• 13 Buchi G. Chu P.-S. Tetrahedron  1981,  37:  4509 
• 14 Mattay J. Runsink J. Hertel R. J. Photochem.  1987,  37:  335 
• 15a Spangler LA. Swenton JS. J. Org. Chem.  1984,  49:  1800 
• 15b Rabideau PW. Tetrahedron Lett.  1991,  32:  3969 
• 16 Mizuno K. Yasueda M. Otsuji Y. Chem. Lett.  1988,  229 
• 17 Rabideau PW. Marcinow Z. Tetrahedron Lett.  1988,  29:  3777 
• 18 Bartoli G. J. Org. Chem.  1987,  52:  4381 
• 19 Paquette LA. Yan TH. Wells GJ. J. Org. Chem.  1984,  49:  3610 
• 20 Grignon-Dubois M. Dunogues J. Calas R. Synthesis  1976,  737 
• 21 Ohno M. Ohshiro Y. Synlett  1991,  919 
• 22 Wender PA. Howbert JJ. Tetrahedron Lett.  1983,  24:  5325 
• 23 Bryce-Smith D. Drew MGB. Fenton GA. Gilbert A. Proctor A. J. Chem. Soc., Perkin Trans. 2  1991,  779