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. 

Alder-Rickert cleavage was also examined as a potential route for 100 and 102, but the required precursors could not be synthesized. Bis-methano[14]annulene 105 added dicyanoacetylene in the wrong sense, and did not yield 106, which could have served as precursor of 102. Similarly, the attempted Diels-Alder reaction of the bridged cyclopropafl OJannulene 107 with dlmethoxycarbonylacetylene, which should furnish 108, produced only decomposed material. This is consistent with the observation of Halton and Russel that 107 does not add to 4-phenyl-1,2,4-tria-zoline-3,5-dione. In order to circumvent the low reactivity of 107 in cycloaddi-... 

Other approaches to alkylidenecycloproparenes have been attempted without success. Aromatization of appropriate alkylidenecyclopropanes or their precursors could not be realized, and flash vacuum pyrolysis of methylene phthalide and 3-methylene-2-coumaranone afforded rearrangement products rather than alkylidenecycloproparenes via extrusion of 002. The photochemical or thermal decomposition of the sodium salt of benzocyclobutenone p-toluenesulfonyl hydrazone led to products derived from dimerization of the intermediate benzocy-clobutenylidene, or from its reaction with the solvent, but no ring-contracted products were observed. When the adduct of methylene-l,6-methano[10]annulene to dicyanoacetylene (249) was subjected to Alder-Rickert cleavage, phenylacety-lene (250) was formed, which derives reasonably from the parent 234. ... 

It had previously been shown that 2,4,6-triphenyl-l,3-azaarsenin 36 could be converted to highly substituted arsenins 38 via a reaction with dienophiles followed by Alder-Rickert cleavage of the intermediate adduct as illustrated in... 

Alder-Rickert Cleavage of 1,6-Methano 10]annnlene Adducts... 

The Alder-Rickert cleavage of cycloadducts of acetylenedicarbonitrile or dimethyl acetylene-dicarboxylate to l,6-methano[10]annulenes results in formation of benzocyclopropenes or cycloproparenes, respectively, according to the general scheme (for examples, see Table 1). 

Table 1. Benzocyclopropenes by Alder-Rickert Cleavage of Locked Norcaradienes...

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%. 

The synthetic breakthrough in cycloproparene chemistry was achieved by Anet and Anet in 1964 who prqtared l,l-dimethyl-3-methoxycarbonylbenzocyclo-propene (9) by irradiation of the substituted 3H-indazole 8. The parent benzocyclopropene (1) was obtained a year later by Vogel et al. by retro-Diels-Alder reaction (Aldw-Rickert cleavage) of 10. ... 

Alder-Rickert (retro Diels-Alder) cleavage of the formal cyclopropene adduct 58 (prepared by cycloaddition between norcaradiene and dimethyl acetylenedicarboxylate)... 

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