[Structure: see text] A TiCl4-promoted tandem semipinacol/Aubé's type intramolecular Schmidt reaction of alpha-siloxy-epoxy-azide has been designed and developed to be a general method for efficient construction of azaquaternary carbon units. As applicable examples, some key tricyclic azaquaternary skeletons incorporated in many important alkaloids, such as cephalotaxine, stemonamine, erythrinan, and homoerythrinan alkaloids, have been constructed.