Indolizinium salts

Bromolaudanosine, on treatment with potassamide or sodamide in liquid ammonia, yields the dibenzo[ >,g]indolizinium salt (21), the reaction presumably proceeding through the aryne, together with aminolaudanosine and the indoline (22) and the indole (23).32 Photolysis of laudanosine methiodide yields the base (24 R = Me) in methanol and (24 R = H) in water. The latter, on heating with... 

In contrast to 2-phosphaindolizines (11) which are stable in dry air and which cannot be alkylated <91CB475>, 1-phosphaindolizines (12) and 1-arsaindolizines (25) readily decompose in air and form indolizinium salts with methyl iodide <87TL1511>. This is in accordance with the higher positive charge at the phosphorus atom in (11) than in (12) (see Section 3.16.2.1). 

A palladium-catalyzed domino sequence for the synthesis of polysubstituted indol-izinones 229 from tertiary propargylic alcohols 228 and aryl iodides was developed by Kim and Kim [86] (Scheme 6.63). The authors reasoned that arylpaUadium species formed in situ by oxidative addition of Pd(0) to aryl haUde could coordinate with the triple bond and activate it. Then, nucleophilic attack of the neighboring pyridine group to the alkyne moiety would generate the indolizinium salt intermediate 231, followed by reductive elimination to furnish intermediate 232. Finally, 1,2-migradon would afford the desired indolizinones. 

Reaction with vatious nucleophilic reagents provides several types of dyes. Those with simple chromophores include the hernicyanine iodide [16384-23-9] (20) in which one of the terminal nitrogens is nonheterocyclic enamine triearbocyanine iodide [16384-24-0] (21) useful as a laser dye and the merocyanine [32634-47-2] (22). More complex polynuclear dyes from reagents with more than one reactive site include the trinuclear BAB (Basic-Acidic-Basic) dye [66037-42-1] (23) containing basic-acidic-basic heterocycles. Indolizinium quaternary salts (24), derived from reaction of diphenylcyclopropenone [886-38-4] and 4-picoline [108-89-4] provide trimethine dyes such as (25), which absorb near 950 nm in the infrared (23). 

The immonium salts derived from 1-azabicycloalkanes have very characteristic NMR spectra (115,116), as illustrated by the spectrum of -indolizinium perchlorate. Assignments of the peaks at t = 5.85 and +... 

Indolizine and its simple alkyl derivatives are sensitive to light and to aerial oxidation, which lead to destruction of the ring system. Catalytic reduction in acidic solution (reduction of the indolizinium cation) selectively saturates the pyrrole ring, giving a pyridinium salt complete saturation, affording indolizidines, results from reductions over platinum. ... 

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