From Diazo Compounds and Alkenes Bearing Suitable Leaving Groups

From Diazo Compounds and Alkenes Bearing Suitable Leaving Groups 

Alkenes substituted with potential leaving groups are masked alkynes and are thus useful alternative dipolarophiles. They react with diazo compounds, producing pyrazolines, which can undergo elimination to give 3//-pyrazoIes. 

Elimination may occur spontaneously during the reaction but generally has been carried out subsequently, sometimes accompanied by rearrangement to the l//-pyrazoIe. 

An advantage of the method is that in all reported examples only one sense of cycloaddition has been observed. 

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