We reported the first example of the construction of C–C bonds using unprotected amino acids as stable alkyl/acyl radical precursors under metal-free conditions. This novel, environmentally friendly, and one-pot procedure was successfully applied to the radical alkylation or acylation/cyclization of isocyanides, which selectively affords 6-alkyl or acyl phenanthridines, depending on the substituent pattern of amino acid side chain groups.