Process for the Preparation of Methylenecyclopropane

Binger, US Patent 5,723,714 (March 3, 1998) Assignee Studiengesellschaft Kohle mbH. 

Potassium bis(trimethylsilyl)amide (0.31 mol) was dissolved in 100 ml o-xylene and /3-methallylchloride (0.25 mol) added dropwise at 145 °C over 60 minutes. The released gas was trapped at —78°C in a cold trap of which 97% consisted of methylene-cyclopropane and 3% of 1-methylcyclopropane. 

Bis(trimethylsilyl)-amide Cation Reaction Solvent Product Yield (%) Methylene Cyclopropane Composition (%) 1-Methyl-cyclopropane Composition (%) 

Methylcyclopropene has also been prepared by reacting 3-chloro- or bromo-2-methylpropene with sodium amide or lithium di-isopropylamide in mineral oil and the product trapped in an a-dextrin matrix (3). In addition, it has been prepared in mineral oil using catalytic amounts of hexamethyldisilazane (4) as described below  

Sodium amide (2.79 mol) and 110 ml light mineral oil were heated to 45 °C whereupon hexamethyldisilazane (0.03 mol) was added. Over 50 minutes, 3-chloro-2-methylpropene (2.23 mol) was slowly added and the evolving gas scrubbed with water then condensed in a dry ice cooled trap. The total product weight consisted of 39.5 g of which 39.3 g comprised 1-methyl-cyclopropene. 

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