Heterocyclics thiochromans

Hydrazones of thiochroman-4-ones are converted into thiochromans under Wolff-Kishner-Huang conditions65 and into the azo dimers by silver oxide.66 Fisher indolization of the phenylhydrazones (33) gives 6,ll-dihydrobenz[6]indolo[2,3-d]thiopyrans (34), which by hydride loss form the thiopyrylium salts (35), or on dehydrogenation produce the pseudoazulenes (36) (heterocyclic analogs of the carcinogen, benz[a]-carbazole), as shown in Scheme 6.87-73... 

The present volume encompasses a wide range of heterocyclic chemistry. Syntheses of heterocycles from thioureas are reviewed by T. S. Criffin, T. S. Woods, and 1). L. Klayman, while S. W. Schneller describes the chemistry of benzothiins and their derivatives (thiochromans, thiochromones, and thio-chromanones). Developments in chrom-3-ene chemistry are reviewed by L. Merlini. F. D. Popp contributes a chapter on the isatins. A discussion of theoretical aspects of the tautomerism of pyrimidines, by J. S. Kwiatkowski and B. Pullman, follows up a corresponding earlier contribution (Vol. 13) on tautomeric purines. In the final chapter P. and D. Cagniant describe the natural occurrence and synthesis of the benzofurans. 

An interesting conversion of thiochromane to 1-benzthiepane has been reported <95TL4459>. Cleavage of the heterocyclic ring with lithium 4,4 -di-fert-butylbiphenylide and treatment with formaldehyde gives 2-(4 -hydroxybutyl)thiophenol which cyclises on heating in acid and subsequent base treatment. 

The enantiomers of thiochroman 1-oxide have been obtained by oxidation of thiochroman in the presence of (R,R)-l,2-diphenylethane-l,2-diol (DPED) or L-diethyl tartrate. In the case of the enantioselective oxidation of thiochroman-4-one, (R,R)-DPED and (V,V)-DPED were used as the chiral inducers <2002CH400>. Fligh yields of both (—)-(R)-thiochroman 1-oxide and (—)-(R)-thiochroman-4-one 1-oxide and with enantioselectivities of 98% and 96%, respectively result from the reaction of H202 with the heterocycles when significant amounts of chloroperox-idase are used as catalyst <1998CH246>. 

Heterocyclic azides can give good yields of aziridines (Scheme 21), but the reactions can give other products, Spending on the precise combination of starting materials. The reaction shown in Scheme 21 is believed to occur via a nitrene, not a triazoline, and is favored by electron>poor alkenes (in this case, electron-rich alkenes give much isomeric thiochroman). 

Anodic fluorination of 3-benzyl-1-thiochromones and thiochroman-4-ones, in particular, of (Z)-3-benzylidene-2,3-dihydrothiochroman-4-one, yields two monofluoro derivatives due to substitution of hydrogen at the a position relative to the sulfur atom of the heterocyclic ring and fluorine addition at the double bond (01JOC7030) (Scheme 7). 

Synthesis of chiral heterocycles by domino organocatalytic processes has also been intensively studied. In particular, various benzo-fused heterocycles, such as chiral chromans, " thiochromanes, hydro-quinolines, dihydropyranes, or thiopyranes were investigated. These organocatalytic sequence were typically initiated by a hetero-Michael addition of a sulfur, oiqrgen or nitrogen nucleophile, which triggers the formation of an enolate/enamine that adds to the ortho electrophile terminating the cascade reaction. An elimination step or an additional cyclisation step follows (Scheme 8.25). 

The structures of several sulphur heterocycles have been determined using A -ray methods, including the thian-4-ol (85), which still showed a flattened chair form, thian-4-ones, e.g. (86), 2-chloro-4-t-butylthian 1-oxides, 1-methylthiolanium iodide,the rra/is-2-thiadecalin derivative (87), cis- and rrans-fused tricyclic compounds (88), the bicyclic dihydrothiopyran (89), thiochroman-4-one 1,1-dioxide, 4-bromothiochroman 1,1-dioxide, the degradation product from thiamine (90), and the tricyclic sulphur-containing sesquiterpene (91). ... 

Gao, Y., Ren, Q., Wu, H., Li, M., Wang, J. (2010). Enantioselective heterocyclic synthesis of spiro chromanone-thiochroman complexes catalyzed by a bifunctional indane catalyst. Chemical Communications, 46, 9232-9234. 

Geranyl phenyl sulphides or sulphones, Me2C=CHCH2CMe=CHCHXY (33 X = H Y = SPh or SOjPh), cyclized to cyclocitral derivatives under acid conditions, whereas the corresponding dithioacetal (33 X = Y = SPh) gives the thiochroman (34). The novel heterocycles (35) have been prepared by standard methods from the corresponding tellurochromanones. The critical step in the synthesis of the latter consists of reduction of the appropriate diaryl ditelluride with borohydride and subsequent reaction with 3-chloropropionic acid under carefully controlled conditions. 

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