β-Oxodithioesters

Introduction

β-Oxodithioesters 1, sulfur analogues of β-ketoesters, are important synthons frequently used for the synthesis of heterocycles. 1 can easily be synthesized by the reaction of methyl ketones (or active methylene compounds) with dialkyl-, allyl-, or benzyl trithiocarbonates in the presence of NaH (Scheme [1]).[1] These versatile reagents are yellow and have a low melting point as well as an offensive odor.

Scheme 1 Synthesis of β-oxodithioesters

Other synthons such as β-oxothioamides and S,S- or N,S-acetals can also be synthesized from 1.[2] [3] Figure [1] shows the reactivity profile of β-oxodithioesters: the carbon atoms of the carbonyl and thiocarbonyl groups are electrophilic centers while oxygen, sulfur, and the carbon of the active methylene group are nucleophilic centers.

Figure 1 Reactivity profile of β-oxodithioesters

Abstracts

(A) Samuel et al.[4] reported the synthesis of thiophenes by alkylation of β-oxodithioester with α-haloketones. Depending on the combination of base and solvent, differently substituted thiophenes are obtained.
(B) β-Oxodithioester in the presence of DMAP reacted with dialkyl acetylenedicarboxylate to give 2,3,4-trisubstituted thiophenes in high yield in short reaction times.[5]
(C) Samuel et al.[6] have reported the synthesis of 2-ylidene-1,3-oxathioles in good yield using β-oxodithioester and α-haloketone in the presence of NaH in toluene.
(D) Chromene and benzochromene-2-thiones were efficiently synthesized in high yield by the reaction of β-oxodithioester and 2-hydroxy benzaldehyde/naphthaldehyde under solvent-free conditions using SiO2·H2SO4 as the catalyst.[7]
(E) A facile and efficient protocol for the synthesis of benzo[f]chromene from β-oxodithioester and β-naphthol has been developed using catalytic InCl3. In this reaction, transesterification was also observed.[8]
(F) Singh et al.[9] have presented the synthesis of highly functionalized thiopyran/thiochromene derivatives when β-oxodithioester was treated with aldehyde and an active methylene compound containing a cyano group[9a] or a 1,3-cyclohexanedione.[9b]
(G) A green and highly efficient method for the regioselective synthesis of imidazo[1,2-a]pyridine derivatives using β-oxodithioester, cyclic N,N-acetal and aldehyde has been presented by Li and co-workers.[10]
(H) Li and co-workers[11] also reported an unprecedented, three-component cascade synthesis of imidazo[1,2-a]thiochromeno[3,2-e]pyridines under solvent-free conditions without using any transition-metal catalyst.
(I) Dihydropyrimidinones and dihydropyridopyrimidinones were synthesized via one-pot, three-component cyclocondensation of ­aromatic aldehydes, β-oxodithioesters, and urea/6-amino-1,3-dimethyluracil in the presence of a recyclable SiO2·H2SO4 acid catalyst.[7]
(J) The treatment of pyridine substituted β-oxodithioester with 2-bromoacetophenone led to the formation of highly substituted indolizine in moderate to good yield. The reaction was performed in chloroform in the presence of catalyst DBU/p-chloranil. Kakehi et al.[12] have synthesized and analyzed the conformation of these molecules.

• References

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• 2a Rahman A, Ila H, Junjappa H. Synthesis 1984; 250
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