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Photochemical Formation of Heteromethylenecyclopropanes, 27 . Annulated Tetrazolium Salts
Author(s) -
Quast Helmut,
Balthasar Jürgen,
Fuss Andreas,
Nahr Uwe,
Nüdling Wolfgang
Publication year - 1997
Publication title -
liebigs annalen
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 0947-3440
DOI - 10.1002/jlac.199719970408
Subject(s) - chemistry , iodide , intramolecular force , bromide , halide , alkylation , medicinal chemistry , methyl iodide , cycloaddition , alkyl , ethyl iodide , organic chemistry , catalysis
Abstract Lithiation of the annulated tetrazoles 6a, c with butyllithium yields the N ‐lithiotetrazoles 7a, c which are allowed to react with alkyl halides. Alkylation at the α‐carbon atom is observed in the reaction with methyl iodide (→ 6b, d ), 1‐bromo‐2‐chloroethane ( 7c→14a ), and 1,3‐dibromopropane (→ 16, 17 ), while 1,2‐dichloro‐ and 1,2‐dibromoethane give other products, viz. 11–13 . Quaternisation of 6 with dimethyl sulphate affords mixtures of 1‐methyl‐ ( 1 ) and 2‐methyltetrazolium salts ( 8 ) (3:1–4:1) from which the hexafluorophosphates 1 PF 6 are obtained by crystallisation. Methyl triflate converts the ω‐azidonitriles 9 into the N ‐methylnitrilium triflates 10 which immediately undergo an intramolecular 1,3‐dipolar cycloaddition to afford the 1‐methyltetrazolium triflates 1 F 3 CSO 3 . Cyclisation of 16 by intramolecular N ‐alkylation furnishes the bisannulated tetrazolium bromide 3a · Br. Attempts to obtain the lower homologue 15 , either from 14a or from 17 , met with failure. Instead, 17 rearranges via 15b into 14b . The α‐branched tetrazole 24 is synthesised from ethyl cyanoacetate and the bromide 18 . Double cyclisation of 24 affords the bisannulated tetrazolium chloride 3b · Cl. The analogous scheme, envisaged for the synthesis of the lower homologue 32 , failed in the last step owing to the high strain of this system.