A new method for the preparation of 2-thio substituted furans by methylsulfanylation of gamma-dithiane carbonyl compounds.
Several related methods for the preparation of differentially substituted 2-thiofurans are described. The general procedure involves the formation of a thionium ion from a gamma-dithianyl substituted carbonyl compound followed by cyclization of this reactive intermediate onto the tethered carbonyl group. Two methods for thionium ion generation were explored. One of these involved an acid-catalyzed reaction of beta-ketenedithioacetals, prepared from the condensation of 2,2-bis(methylsulfanyl)acetaldehyde with a variety of ketones. Cyclization followed by loss of methane thiol gave 2-thiofurans 17, 18 and 23, 24 in 70-90% yield. Attempts to prepare 5-heteroatom substituted 2-thiofurans from the corresponding beta-ketenedithioacetal amides or esters were unsuccessful, leading to 1,2-thio rearranged products. A more successful route involved the reaction of beta-acetoxy-gamma-thianyl carbonyl compounds with dimethyl(methylthio)sulfonium tetrafluoroborate (DMTSF). Treatment of the dithiane with this reagent resulted in the smooth generation of a thionium ion. Cyclization followed by loss of acetic acid afforded thiofurans 17, 18, 23, 47-49, 51, and 61-64 in 40-100% yield. The N-butenyl substituted thioamido furan furnished a rearranged hexahydropyrroloquinolin-2-one in high yield when heated at 110 degrees C.
Padwa
Albert
A
Department of Chemistry, Emory University, Atlanta, Georgia 30322, USA.
Eidell
Cheryl K
CK
Ginn
John D
JD
McClure
Michael S
MS
D002384:Catalysis; D002625:Chemistry, Organic / Q000379:methods; D005663:Furans / Q000138:chemical synthesis* / Q000737:chemistry; D007659:Ketones / Q000138:chemical synthesis* / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D008698:Mesylates / Q000737:chemistry*; D015394:Molecular Structure; D013455:Sulfur / Q000737:chemistry*
D005663:Furans; D007659:Ketones; D008698:Mesylates; D013455:Sulfur