1.Thermocatalytic reaction of alkyl diazoacetates with an excess of gaseous divinyl at atmospheric pressure proceeds with the formation of the corresponding esters of isomeric 2-vinylcyclopropanecarboxylic acids with the trans-isomer predominating. The maximum yields (∼ 50%) are obtained when methyl diazoacetate is used with CuO as the catalyst.2.A simple method for the preparation of 2-ethynylcyclopropanecarboxylic acid and its esters is proposed. It consists in the dehydrobromination with aqueous-alcoholic KOH of 2-(1,2-dibromoethyl)cyclopropanecarboxylic acid or its esters, obtained by the low-temperature bromination of 2-vinylcyclopropanecarboxylic acid or its esters.3.By the oxidative dimerization of 2-ethynylcyclopropanecarboxylic acid, the previously unknown bis (2-carboxycyclopropyl)diacetylene was obtaine