Pteridines. Part CXIX.

Abstract

A variety of pyrimidine precursors 12–25 were converted into a series of new 7‐hydroxylumazines (=7‐hydroxypteridine‐2,4(1H,3H)‐diones) 26–35 which functioned as starting materials for the transformation into the corresponding 7‐chlorolumazines 36–45. Subsequent reaction with hydrazine led to the 7‐hydrazinolumazines 46–55 which gave on nitrosation the 7‐azidolumazines 1 and 56–64. These compounds were subjected to short heating in xylene whereby 1 and 56–61 showed a new pteridine–purine interconversion in forming a new type of 1,3‐disubstituted or 3‐substituted xanthin‐8‐amine‐derived nitrilium ylides (2,3,6,7‐tetrahydro‐N‐methylidyne‐2,6‐dioxo‐1H‐purin‐8‐aminium ylides) 11 and 65–70. The presence of an additional 6‐alkyl substituent in the 7‐azidolumazines 63 and 64 or of an unsubstituted N(3) position in 62 caused further rearrangement to xanthine‐9‐carbonitriles 71–73. Prolonged heating of 7‐azido‐1,3‐dimethyllumazine (1) also afforded theophylline‐9‐carbonitrile (=1,2,3,6‐tetrahydro‐1,3‐dimethyl‐2,6‐dioxo‐9H‐purine‐9‐carbonitrile; 5). The nitrilium ylide function was established by NMR and UV spectra as well as by elemental analyses. Confirmation of the nitrilium ylide structures was suggested by the result of the heating of 1,3‐dimethyl‐N‐methylidynexanthin‐8‐aminium ylide 11 in EtOH or of 1 in pentan‐1‐ol leading to 8‐aminotheophylline (=8‐amino‐3,7‐dihydro‐1,3‐dimethyl‐1H‐purin‐2,6‐dione; 74).

12-(N-Methylnitrilium)monocarba-closo-dodecaborate Ylide

“…Numerous nitrilium ylides are known, such as nitrile oxides, 22 sulfides, 23 and ylides carrying carbocyclic 24 or heterocyclic 25,26 anionic groups at the cyano nitrogen, as well as nitriliumphosphane ylides, which are usually used as reactive intermediates generated in situ. 27−29 However, only a limited number of stable nitrilium ylides have been isolated and thoroughly characterized.…”

“…27−29 However, only a limited number of stable nitrilium ylides have been isolated and thoroughly characterized. 25,26,30 Most nitrilium ylides carry their negatively charged group at the nitrogen atom and allow this group to conjugate with the CN group. They display a characteristic IR stretch band at 2150−2200 cm −1 , strongly redshifted from an ordinary cyano group of nitriles, suggesting a description of bonding in terms of cumulated double bonds.…”