7-Substituted 4-styrylcoumarins

The chiral holmium(III)-complex-catalysed Diels-Alder cycloaddition of siloxyvinylindoles (70) with e-deficient olefins (71) formed exo-substituted hydro-carbazoles (72) in up to 99% yield and 94% ee. Alkylation of these cycloadducts gave tricyclic compounds (73) with four continuous chiral centres (Scheme 20). The thermal 4-i-2-cycloaddition reaction of 7-substituted 4-styrylcoumarins with A-phenylmaleimide and tetracyanoethylene in nitrobenzene yielded 3,4-annulated coumarins. The thermal Diels-Alder cycloaddition of ( )-l,3-dihydro-3-phenacylidene-2//-indol-2-ones (74) with l,2-dihydro-2-oxospiro[3//-indole-3,2 -[2H,9a//-pyrido[2,l-fe][l,3]oxazines]] (75) produced complex dispirooxindoline fused [l,3]oxazines (76) with high regio- and stereo-selectivity (Scheme 21). " ... 

Keywords fluoro-substituted styrylcoumarin, [2+2]photodimerization, cyclobutane... 

Vishnumurthy, K., Guru Row, T. N., and Venkatesan, K., Studies in crystal engineering crystal packing, topological photodimerization and structure-reactivity correlations in fluoro-substituted styrylcoumarins, /. Chem. Soc., Perkin Trans. 2, 615-619,1997. 

It appears reasonable to assume from the dramatic changes in the supramolecular assembly of fluorine-substituted coumarin, 4-styrylcoumarin, and 1,4-diphenyl-butadiene that significant contributions to the lattice energy arise... 

Row, T. N. G. (1999). Hydrogen and fluroine in crystal engineering systematics from crystallographic studies of hydrogen bonded tartrate-amine complexes and fluro-substituted coumarins, styrylcoumarins and butadienes. Coord. Chem. Rev., 183, 81-100. [236]... 

The effects of fluorine substitution on crystal packing and topological photodimerization have also been investigated for styrylcoumarins. " Styrylcoumarin 3 yields the centrosymmetric (a-mode, anti-head-to-tail [HT]) photodimer 5 when irradiated in the solid state however, the inclusion of a fluorine substituent dramatically alters the packing mode and steers molecules 4a and 4b to form stereospecdfic photodimers 6a and 6b (P-mode, sy -head-to-head [HH]) by reaction at the styrenic double bonds. 

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