Novel Iminium Ion Equivalents Prepared through C−H Oxidation for the Stereocontrolled Synthesis of Functionalized Propargylic Amine Derivatives

Access to stereochemically complex, polyfunctionalized amine derivatives is made possible using novel oxathiazinane N,O-acetal starting materials. These heterocycles are prepared through intramolecular sulfamate ester C−H insertion with a Rh2+-carboxylate catalyst and PhI(OAc)2 as the terminal oxidant. Such compounds function as unique iminium ion equivalents to which nucleophilic alkynylzinc reagents add smoothly in the presence of BF3·OEt2. The coupled products are isolated in high yield (63−92%) and with good levels of diastereoinduction (6 → 20:1). The alkyne-substituted oxathiazinanes serve as versatile building blocks and may be further manipulated through nucleophilic ring-opening reactions of the sulfamate core. The efficient construction of 1,7,8-trihydroxyindolizidine in six steps and in 34% overall yield highlights the power of these combined methods for synthesis.