[3 + 2]-Annulation of Prop-2-ynylsulfonium Salts: Access to Hydroindol-5-ones Containing a Methylthio Group.

An unprecedented [3 + 2]-annulation of prop-2-ynylsulfonium salts and p-quinamines was developed, affording a series of hydroindol-5-ones with a methylthio group in moderate to good yields under mild conditions. In this reaction, the prop-2-ynylsulfonium salt acts as a novel C2 synthon and sulfide does not serve as a leaving group, which provides facile access to organosulfur compouds.