Chromenes thiochromenes

V I. Minkin, B. Y. Simkin, L. E. Nivorozhkin, and B. S. Luk yanov, Photo- and thermochromic spirans. IV. Theoretical study of electron structure and spectra ofvalence isomers of 27/-chromenes, thiochromenes and 1,2-dihydroquinolines, Khim. Geterotsikl. Soedin. 1974, 67-75 Russ. Chem, Rev. 59, 685-692 (1990)]. 

The colored form of 2,2-diphenyl-2//-thiochromene (thio analogue of chromene) absorbs at 650 nm in 3-methylpentane at 77 K.71... 

ThrePHOX 6b proved to be a valuable tool in the reduction of chromenes 71a-k, all of which were reduced in greater than 90% enantioselectivity. The very electron-rich thiochromene 71h required higher temperature, and lower conversion was observed, but the enantioselectivity remained in the useful range (Table 13) [96]. 

Thiocoumarin reacts with phenylmagnesium bromide to give a mixture of 2-phenyl-A -thiochromene and thioflavone, the latter product being presumed to arise by oxidation of 4-hydroxy-2-phenyl-A -chromene, formed via a thiopyrylium cation. 4-Hydroxythiocoumarin has been acetylated at the 3-position, by treatment with acetic acid and phosphorus oxychloride reactions of the product with amines and with phenylhydrazine have been studied. ... 

Pummerer reactions with thiochroman 1-oxides normally yield A -chromenes, except when the 2-position is blocked. The thiochromene (57), produced in this way, undergoes the photochemical rearrangement shown. A different stereoisomeric form of compound (58) is produced... 

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