Synthesis Alder-Rickert cleavage

Alder-Rickert cleavage has not been widely used for cycloproparene synthesis, since the preparation of the precursors is often tedious, except for the simple cases like 7,7-difluorobenzocyclopropene (21). The approach offers, however, decisive advantages in special situations. If the Alder-Rickert cleavage is carried out under flash-vacuum pyrolysis conditions, the products may be isolated under neutral conditions and at low temperature. Thus the synthesis of the highly reactive li/-cyclopropa[a]naphthalene (56) by pyrolysis of 68 has been achieved by this approach. Several other approaches to 56 failed. 

A variety of diverse synthetic methods have been empioyed for the preparation of cyclopropane (1 j. Schlatter and Demjanov and Dojarenko pyrolyzed cyclopropyltrimethylammonium hydroxide at 320°C using platinized asbestos as the catalyst. About equal amounts of cyclopropene (1) and cyclopropyidimethylamine are formed, contaminated with some dimethyl ether and ethylene. Treatment with dilute hydrochloric acid removed the amine from the gas stream and 1 was separated from the other products by gas chromatography. Alder-Rickert cleavage of the Diels-Alder adduct formed from cycloheptatriene and dimethyl acetylenedicarboxylate resulted only in the formation of a polymer and trace amounts of 1. A simple approach by Closs and Krantz based on the synthesis of 1-methylcyclopropene involved the addition of allyl chioride to a suspension of sodium amide in mineral oil at 80°C. Under the conditions employed, 1 could readily escape from the reaction mixture. Though a number of variations were tried, the yield of 1 never exceeded 10%. 

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