Studies On The [4+2] Cyclization Between Vinylogous Thiol Esters And Diacetyl Ketene Dithioacetals

Vinylogous thiol esters are kind of active intermediates in organic synthesis. Varioustransformations from vinylogous thiol ester could be achieved for its versatile reaction sites.Recently, the synthesis and properties of vinylogous thiol ester bearing1,4-dicarbonyl motifhave attracted much attentions for their wide application in the synthesis of five-memberedheterocyles such as furans, pyrroles and thiophenes via Paal-Knorr reaction. The structure ofvinylogous thiol ester can be viewed as an insertion of carbon-carbon double bond into theC-S bond of thioester, which brings some specialties on the carbon-carbon double bond. Thus,we focused on the carbon-carbon double bond in vinylogous thiol ester as a two-carbonsynthon and investigated their [2+4] annulation with diacetyl ketene dithioacetal.Our group has been dealing with ketene dithioacetals chemistry for more than twentyyears, and has developed our characteristic synthetic methodologies for carbo-andhetero-cycles, such as the [5+1] annulation for the synthesis of six-membered carbo-/hetero-cycles with alkenoyl ketene dithioacetals as the five-carbon synthons. Based on thesedevelopments, herein, we investigated a new tandem [4+2] annulation with vinylogous thiolester as the two-carbon synthon and diacetyl ketene dithioacetals as the four-carbon synthon.As a result, poly-substituted cyclohexenones were efficiently constructed in one step.Although many synthetic methods have been reported for poly-substitutedcyclohexenones, they often need multi-step procedures or use expensive reagents, requiringtransition metal catalysis. In this thesis, we provided a new and simple method for theconstruction of six-membered carbocycles without using transition metal catalysis. It’sefficient and environment-friendly.