A facile domino protocol for the stereoselective synthesis of trans-2,3-dihydrobenzofurans and cis-5,6-dihydrofuro[2,3-d]pyrimidines

A facile protocol for the stereoselective construction of trans-2,3-dihydrobenzofurans and cis-5,6-dihydrofuro[2,3-d]pyrimidines from the reactions of 2,2′-sulfonylbis(1,3-diarylprop-2-en-1-ones) with cyclic 1,3-diketones, viz. cyclohexane-1,3-diones, barbituric acid, and 2-thioxodihydropyrimidine-4,6(1H,5H)-dione in the presence of DBU in ethanol is described. This transformation presumably occurs via domino Michael addition-proton exchange-annulation via intramolecular displacement sequence.     

Novel Domino Reactions of (Z,Z)-2,2′-Thiobis(1,3-diarylprop-2-en-1-ones) with Acetylacetone and Ethyl Acetoacetate: Stereoselective Synthesis of Highly Functionalized Dihydrofurans

The domino reactions of (Z,Z)-2,2′-thiobis(1,3-diarylprop-2-en-1-ones) with acetylacetone and ethyl acetoacetate in the presence of sodium ethoxide afforded the corresponding 4,5-dihydrofurans stereoselectively in moderate yields presumably via a Michael addition–enolization–displacement sequence.     

A Diastereoselective Synthesis of Novel Multifunctional Thianes

The reaction of 2,2′-thiobis(1,3-diarylprop-2-en-1-ones) with malononitrile in the presence of sodium ethoxide under both thermal and solvent-free microwave conditions afforded a series of hitherto unknown 2e,6e-diaroyl-3e,5e-diaryl-4,4-dicyanothianes diastereoselectively in good yields via a double Michael addition. The structures of all the compounds have been elucidated by IR, ¹H NMR, ¹³C NMR, and elemental analysis.     

Stereoselective Synthesis of Polyfunctionalized Nitrothianes: Enhancement of Stereoselectivity by Microwaves

The Michael addition of nitromethane to (Z,Z)-2,2′-thiobis(1,3-diarylprop-2-en-1-ones) in the presence of NaOEt in dimethylformamide (DMF)/alcohol under thermal conditions affords a diastereomeric mixture of 2a,6e-diaroyl-3a,5e-diaryl-4e-nitrothianes and 2e,6e-diaroyl-3e,5e-diaryl-4e-nitrothianes with a dr of ～3:1/4:1 respectively. This reaction under microwave irradiation in DMF/alcohol afforded solely 2a,6e-diaroyl-3a,5e-diaryl-4e-nitrothianes, disclosing enhancement of stereoselectivity by microwaves.

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