Amidine Dications as Superelectrophiles

Abstract

2-Dimethylalkylammonium pyridinium and 2-dimethylalkylammonium pyrimidinium ditriflate salts are very powerful methylating agents toward phosphorus (triphenylphosphine) and nitrogen (triethylamine) nucleophiles. In competition experiments with triethylamine as nucleophile, these N-methyl disalts are more reactive methylating agents than dimethyl sulfate. Reaction of the pyridinium dications with water as an oxygen nucleophile leads to attack at the 2-position of the heteroaromatic ring and displacement of an ammonium group; 2-hydroxypyridinium compounds are formed in the first instance, which are easily converted to 2-pyridones. Extending the scope of the reactions, a tricationic 2,6-bis(dimethylalkylammonium)pyridinium salt has also been prepared and characterized and its reactivity as a methylating agent assessed in comparison with that of the dications.

N‐Methylacridinium Salts: Carbon Lewis Acids in Frustrated Lewis Pairs for σ‐Bond Activation and Catalytic Reductions

“…C9 in 6 is strongly pyramidalized (the sums of non‐N bond angles about C9 are 328.20°) and the acridinium moiety folds along the C(1)‐N(1)‐C(9) axis by 20.99° (trans‐annular folding of 1.22° in [ 2 ]SbF 6 ). The donor‐acceptor NC bonds are comparable to those of other alkylated 4‐DMAP compounds consistent with strong dative bonding 23…”

Pushing the Limits of Neutral Organic Electron Donors: A Tetra(iminophosphorano)‐Substituted Bispyridinylidene

“…Gratifyingly, the addition of 1,3‐diiodopropane to two equivalents of this pyridine cleanly afforded the bispyridinium diiodide 3 , which was isolated in 83 % yield. Exclusive alkylation at the pyridyl nitrogen is in line with previous observations involving 2 ,27 but contrasts the analogous reaction with 2‐(dimethylamino)pyridine, where both the pyridyl and exocyclic nitrogen centers were alkylated 28. Subsequently, the reaction of 3 with two equivalents of KN(SiMe 3 ) 2 (KHMDS) cleanly produced the desired iminophosphorano‐substituted donor 4 , though it could only be isolated in low yield (12 %) owing to its poor solubility.…”

Pushing the Limits of Neutral Organic Electron Donors: A Tetra(iminophosphorano)‐Substituted Bispyridinylidene

“…Exclusive alkylation at the pyridyl nitrogen is in line with previous observations involving 2 , 27 but contrasts the analogous reaction with 2-(dimethylamino)pyridine, where both the pyridyl and exocyclic nitrogen centers were alkylated. 28 Subsequently, the reaction of 3 with two equivalents of KN(SiMe 3 ) 2 (KHMDS) cleanly produced the desired iminophosphorano-substituted donor 4 , though it could only be isolated in low yield (12 %) owing to its poor solubility. Nevertheless, the isolated quantities were sufficient to allow for its chemical oxidation with hexachloroethane to 4 2+ -2 Cl − and subsequent electrochemical analysis by cyclic voltammetry.…”