*3.2. General Procedure for the Cycloaddition of Alkenes and α-Nitroketones*

*p*-TsOH (0.500 mmol, 4 equiv) was added to a solution of **1** (0.125 mmol, 1 equiv) or **6** (0.125 mmol, 1 equiv) and **2** (0.625 mmol, 5 equiv) (or **4** (0.625 mmol, 5 equiv) or **8** (0.625 mmol, 5 equiv)) in ACN (0.2 mL). The mixture was then stirred at 80 ◦C until the starting material disappeared as monitored by TLC. Subsequently, the mixture was directly purified by flash chromatography (with ethyl acetate/petroleum ether as the eluent) to obtain the desired product (**3**, **5, 7** or **9**).
