Herein, we present methods for the generation of selenocysteinyl electrophile by weak Lewis acids or oxidants. The electrophilic selenium species were further utilized in 5-endo-dig cyclization reactions with 2-ethynyl phenols, anisoles, and anilines, yielding substituted benzo[b]furans and indoles bearing short selenocysteine-containing peptides. Copper(II) bromide promoted 5-endo-dig cyclization can be successfully applied for protected and unprotected peptides in high yields. Elaborated protocol allows the construction of phenylindeno[1,2-c]chromene moiety in 5-endo-dig/6-endo-dig cascade reactions.