Abstract A general, organocatalytic inverse-electron-demand [3+ 2] cycloaddition reaction between a range of carbonyl compounds and diazoacetates has been developed. This reaction is catalyzed by secondary amines as a “green promoter” to generate substituted pyrazoles with high levels of regioselectivity. It is noteworthy that this [3+ 2] cycloaddition reaction proceeds efficiently at room temperature with a simple and inexpensive catalyst. ...