Reactions of Silica Chloride (SiO<sub>2</sub>Cl)/DMSO, a Heterogeneous System for the Facile Regeneration of Carbonyl Compounds from Thioacetals and Ring-Expansion Annelation of Cyclic Thioacetals
Thioketals without enolizable hydrogens adjacent to a sulfur atom are converted easily to the corresponding ketones in high yields under similar reaction conditions. However, thioketals with enolizable methyl and methylene groups undergo ring-expansion reactions to afford 1,4-dithiepins and 1,4-dithiins in dry CH(2)Cl(2) at room temperature in good yields.
On treatment with tellurium tetrachloride in dichloromethane at room temperature, 1,3-dithiolanes and 1,3-oxathiolanes undergo smooth ring expansion to give dihydro-1,4-dithiin and dihydro-1,4-oxathiin derivatives respectively in good to moderate yields.
A one-pot synthesis of 1,4-dithiins and 1,4-benzodithiins from ketones using the recyclable reagent 1,1′-(ethane-1,2-diyl)dipyridinium bistribromide (EDPBT)
作者:Siva Murru、Veerababurao Kavala、C.B. Singh、Bhisma K. Patel
DOI:10.1016/j.tetlet.2006.12.003
日期:2007.2
the corresponding ketones in one-pot using the recyclable reagent, 1,1′-(ethane-1,2-diyl)dipyridinium bistribromide (EDPBT) is described. This method is mild, simple, environmentally benign and is applied successfully for the ringexpansion of 1,3-dithiolane to 1,4-dithiins and the ringexpansion associated with aromatisation of cyclicketones with or without double bonds in the ring. The main feature
Aldehydes and methyl ketones readily afford 5,6-dihydro-1,4-dithiins that can be converted by n-butyllithium into their corresponding sulfur stabilized carbanions. Coupling of the latter with alkyl halides leads to species having a cis-configurated, disubstituted double bond tied up by the sulfur-containing ring which is known to be susceptible of selective removal.