Cyanoacetylene trimerization

Four mechanisms have been advanced for the prebiotic formation of amino acids. The first involves a cyanohydrin (reaction 2) and a related route (reaction 3) can be invoked to account for the presence of hydroxy acids. These particular reactions have been studied in considerable detail both kinetically and in terms of thermodynamic quantities.347 An alternative route (4) involves the hydrolysis of a-aminonitriles, which are themselves formed directly in anhydrous CH4/NH3 mixtures.344 Cyanoacetylene, formed in CH4/N2 irradiations,349 yields significant amounts of asparagine and aspartic acids (reaction 5). Finally, a number of workers336,350"354 have proposed that HCN oligomers, especially the trimer aminoacetonitrile and the tetramer diaminomaleonitrile, could have been important precursors for amino acid synthesis. Reaction mixtures involving such species have yielded up to 12 amino acids. Table 11 indicates the range of amino acids produced in these kinds of sparking syntheses. Of some interest is the fact that close parallels between these kinds of experiments and amino acid contents of carbonaceous chondrite meteorites exist.331,355,356... 

That strain activation is no prerequisite for a successful addition is shown by offering classical aromatics to cyanoacetylene (1). Thus anthracene (63) provides the expected adducts 65-67 as well as the secondary dinitriles 68 and 69 (Scheme 2-5). As shown by control experiments, 68 is produced by the addition of the diene 63 to 65, and 69 is produced from 67 by electrocyclic ring-opening. The classical [2 -I- 4] cycloaddition product 64 is observed in this case for the first time, and the trimers 51 and 52 are produced in up to 30% yield [14, 47]. 

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