1.4- Dithiin electrophilic addition reactions

Dioxin and 1,4-dithiin both undergo easy electrophilic addition reactions, e.g. of halogens to the double bonds. Alcohols under acid catalysis form ketal addition products. 

The double bonds in 2,3-dihydro-l,4-dioxin, 2,3-dihydro-l,4-oxathiin and 2,3-dihydro-1,4-dithiin undergo standard electrophilic addition reactions. Under acid catalysis, methanol adds to 2,3-dihydro-l,4-oxathiin to give 2-methoxy-1,4-oxathiane (66HC(21-2)842). Various examples are available of reactions of the double bonds with carbenoids to give bicyclo[4.1.0]diheteroheptanes (77LA910,78ZC15), and with alkenes in [2 + 2] cycloadditions (78CB3624). 

A two-sulphur electrophilic addition to alkynes was reported by Bock and coworkers . The reagent is a mixture of the sulphur chloride S2CI2 and aluminium trichloride dissolved in dichloromethane. Initially, 1,2-dithiete 38 is formed, but in the preparative procedure the isolated product is a mixture of 2,6- and 2,5-di-fcr -butyl-1,4-dithiin (39 and 40). When the reaction is performed under nitrogen in a closed tube, the substituted dithiete is oxidized to its radical cation (equation 23). 

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