The cis‐3,4‐disubstituted cyclobutenes (I) undergo 1,3‐dipolar cycloaddition with the un‐ or monosubstituted diazomethanes (II) to form solely the cis‐adducts (III), whereas (I) and diphenyldiazomethane (IV) produce the trans‐adducts (V).
The dichlorocyclobutene (I) is subjected to 1,3‐dipolar cycloaddition reaction with the diazoalkanes (II) or (IV), yielding exclusively the syn‐adducts (III) or (V) and (VIa).
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