10.1021/jo051832o.s003 Akiyuki Hamasaki Akiyuki Hamasaki Richard Ducray Richard Ducray Dale L. Boger Dale L. Boger Two Novel 1,2,4,5-Tetrazines that Participate in Inverse Electron Demand Diels−Alder Reactions with an Unexpected Regioselectivity American Chemical Society 2006 reaction conditions Unexpected Regioselectivity dienophile choices Diel sulfoxides 4 cycloaddition reactions 2006-01-06 00:00:00 Dataset https://acs.figshare.com/articles/dataset/Two_Novel_1_2_4_5_Tetrazines_that_Participate_in_Inverse_Electron_Demand_Diels_Alder_Reactions_with_an_Unexpected_Regioselectivity/3245287 Two new unsymmetrical 1,2,4,5-tetrazines, 3-methylsulfinyl-6-methylthio-1,2,4,5-tetrazine (<b>4</b>) and 3-(benzyloxycarbonyl)amino-6-methylsulfinyl-1,2,4,5-tetrazine (<b>5</b>), were prepared, and the scope of their participation in intermolecular inverse electron demand Diels−Alder reactions was defined. As anticipated, sulfoxides <b>4</b> and <b>5</b> (<b>4</b> > <b>5</b>) display a reactivity that is substantially greater than that of their corresponding sulfides (<b>2</b> and <b>3</b>), being derived from their enhanced electron-deficient character and resulting in a wider range of potential dienophile choices or the use of milder reaction conditions. The cycloaddition reactions were expectedly regioselective, typically producing a single cycloadduct, ensuring their synthetic utility, but both were found to proceed with a regioselectivity opposite what would be anticipated and complementary to that observed with <b>2</b> and <b>3</b>.