S1 Supporting Information Stereospecific Ring Opening and Cycloisomerization of Aziridines with Propargylamines: Synthesis of Functionalized Piperazines and Tetrahydropyrazines Bijay Ketan Das, Sourav Pradhan and Tharmalingam Punniyamurthy* Department of Chemistry, Indian Institute of Technology Guwahati, Guwahati 781039, India Table of Contents 1 General Information S2 2 General Procedure for the Preparation of N-Propargylamines S2-S3 3 General Procedure for the Preparation of N-Tosyl Aziridines S3 4 Procedure for the Preparation of Chiral Aziridine 2b' S3 5 General Procedure for the Synthesis of Tetrahydropyrazine S4 6 General Procedure for the Coupling of Aziridines with Internal Alkynes S4 7 Scale-up Synthesis of Tetrahydropyrazine S4-S5 8 General Procedure for the Stereospecific Coupling of Aziridines with Propargyl Amine S5 9 Crystal Structure and Data of 3a, 4q and 3ae S5-S8 10 HPLC of compound 3b', 3aa' and 3ae' S9-S11 11 Characterization Data of 4a-ac, 3ae-ah, 3b', 3aa', 3ae', 3a, 4b' and 5 S12-S32 12 NMR ( 1 H and 13 C) Spectra of 4a-ac, 3ae-ah, 3b', 3aa', 3a, 4b' and 5 S33-S114