Synthesis and photochemistry of isothiocoumarins fused to an additional pyranone or thiopyranone ring

Abstract

Both 4H,7H-benzo[1,2-c:4,3-c']dithiin-4,7-dione (3) and 4H,7H-thiino[4,3-f][2]benzopyran- 4,7-dione (4) were synthesized from 1,2-bis(2-hydroxyethyl)benzene (7). On irradiation (lambda > 390 nm) in acetonitrile the symmetric tricycle 3 affords selectively the two-fold cis-cisoid-cis dimer 10 while the asymmetric tricycle 4 gives a 5:1 mixture of the cis-cisoid-cis dimers 11 and 12. On irradiation in benzene in the presence of 2,3-dimethylbut-2-ene 3 affords quantitatively a 3:2 mixture of the diastereomeric monocycloadducts 14c and 14t. Similarly, 4 gives a 3:2 mixture of 15c and 15t on irradiation in benzene in the presence of the same alkene, while in the presence of tetrachloroethene 17 is obtained selectively, all these monocycloadducts resulting from chemoselective addition of the alkene to the thiinone C-C double bond of 4, respectively.

Recent Advances in the Synthesis of Cyclobutanes by Olefin [2 + 2] Photocycloaddition Reactions

“…A smooth reaction occurred between isocoumarin 99 and tetrachloroethylene to give product 100 upon direct excitation . Remarkably, 4 H ,7 H -benzo­[1,2- c :4,3- c ′]­dipyran-4,7-dione ( 101 ), which can be considered as a 2-fold isocoumarin, underwent a smooth 2-fold [2 + 2] photodimerization to product 102 . , The authors pointed out, however, that this reaction should rather be envisaged as an initial 1,6-cycloaddition followed by a second (thermal) ring closure.…”

Syntheses of some 3-substituted isothiochromen-1-ones

“…They also occur as mycotoxins, fungal metabolites, and a principal sweetness component of the Japanese sweet tea [6][7][8]. Most methods available for the construction of the thioisocoumarin and thiocoumarin nucleus suffer from one or more drawbacks, such as a multi-step procedure, low yields [9,10], and long reaction time required to obtain a good yield of the desired product, or the use of expensive and hazardous reagents and solvents. For example, 3-arylisocoumarins were transformed into 3-aryl-1-thioisocoumarins by the reaction with phosphorus pentasulfide, which were converted first into 3-aryldithioisocoumarins in a few steps, and then oxidized to 3-aryl-2-thioisocoumarins by potassium permanganate [11,12].…”