1 Introduction Heteroatom-stabilized carbenium ions have been widely recognized as potential electrophilic reagents. However, in contrast with the extensive works on thionium ion series, the highly labile character of selenoxide functionalities has caused 1 Introduction Heteroatom-stabilized carbenium ions have been widely recognized as potential electrophilic reagents. However, in contrast with the extensive works on thionium ion series, the highly labile character of selenoxide functionalities has caused