Deprotonation of hydrazinium dications in the diazoniapropellane series to form bridgehead iminium ions; external and intramolecular trapping

Abstract

The reactions of hexa-alkylhydrazinium dications with bases and nucleophiles are described. 1,5-Diazoniatricyclo[3.3.2.0]decane (1) is hydrolysed rapidly by S_N2 attack on the four-membered ring with ring opening (C–N⁺ cleavage). In all other cases deprotonation at α–C with concomitant N⁺–N⁺ cleavage (E2 reaction) is the only primary process. The cis-1,6-dimethyl-1,6-diazoniabicyclo[4.4.0]decane ion (6), is exclusively deprotonated at a methyl group ( Hofmann orientation). 1,5-Diazaoniatricyclo [3.3.3.0]-undecane (2), 1, 6-diazoniatricyclo [4.3.3.0] dodecane (3), 1, 6- diazoniatricyclo[4.4.3.0]tridecane (4), and 1,6 -diazoniatricyclo[4.4.4.0]tetradecane (5) ions generate bridgehead iminium ions, which may be trapped intramolecularly by the transannular amino group or externally by added nucleophiles. Reaction with cyanide ion gives detailed information on the regio- and stereo-chemistry of the trapping sequence. Although intramolecular/external trapping is truly competitive, the products of these reactions (α-amino-ammonium ions and α-aminonitriles) may be interconverted under different reaction conditions. The solvolysis of 1-(3-phenoxypropyl)-1,5-diazabicyclo[3.3.0]octanium bromide in aqueous 48% HBr is 10³ faster than that of 3-phenoxypropyltrimethylammonium bromide, and the products are consistent with the intermediacy of the dication (2). These observations provide and explanation for the formation of 1,5-diazacyclo-octane in the reaction of 1,3-dibromopropane with hydrazine.