5-(Methylthio)tetrazoles as versatile synthons in the stereoselective synthesis of polycyclic pyrazolines via photoinduced intramolecular nitrile imine-alkene 1,3-dipolar cycloaddition

摘要

A key thioether substituent in readily accessible 2-alkyl-5-(methylthio)tetrazotes enables facile photoinduced denitrogenation and intramolecular nitrile imine 1,3-dipolar cycloaddition to afford a wide range of polycyclic pyrazoline products with excellent diastereoselectivity. The methylthio group red-shifts the UV absorbance of the tetrazole, obviating the requirement in all previous substrate systems for at least one aryl substituent, and can subsequently be converted into a variety of other functionalities. This synthetic platform has been applied to the concise total syntheses of the alkaloid natural products (±)-newbouldine and withasomnine.