The regioselectivity of cycloaddition reactions of trichloronitrosomethane (1) with 2-alkyl (R= Me, Et, i-Pr, t-Bu, CF3, Bz, and Cl) and 2-aryl (Ar= Ph, 4-CH3OPh, 4-CH3Ph, 3-CH3Ph, and 4-ClPh) 1, 3-butadienes is described. The orientation of cycloaddition is substituent