Pharmaceuticals, molecular catalysts, and secondary metabolites often contain nitrogen. The problems faced synthesizing compounds which contain nitrogen was because of the Lewis base reactivity of nitrogen lone pairs, and the acidic protons of some nitrogenous functional groups. We developed two methods for the synthesis of nitrogeous compounds. Additionally, we successfully constructed the heterotetracyclic core of himgaline. The aminal radicals were generated by reduction of the corresponding amidine or amidinium ion. The intermediate radicals participate in C−C bond- forming reactions to produce fully substituted aminal stereocenters. No toxic additives or reagents are required. The regioselectivity and diastereoselectivity was investigated in pyridinium oxide cycloadditions using complex substrates. The reaction is reversible under the reaction conditions. High levels of diastereoselectivity and regioselectivty are observed, which can be attributed to minimization of syn-pentane interactions in the products. The stereo- and region-selective intramoleculer pyridinium oxide cycloaddition successfully forms two bonds and builds four stereocenters in a single step. These key cycloaddition reactions are particularly suitable to the challenge of preparing multiple rings with control of stereochemistry. It has been shown that the new methodology replacing acid-base strategy would enhance the efficiency of alkaloid synthesis.