S. I. Bobrovskii

NMR Spectra of indolizines and their σ complexes

New and previous data on the1H and13C NMR spectra of indolizines with electron-withdrawing groups at C(1), C(3), C(6), and C(8) obtained in our laboratory are reviewed. The chemical shifts in the13C NMR spectra were compared with the total atomic charge values calculated by the MNDO method. Feasibility was demonstrated for the use of PMR spectroscopy to identify isomers for pairs of 1(3)- and 6(8) -substituted indolizines and to establish the protonation site of such compounds. Evidence was obtained for the unexpected ipso protonation in 3-substituted indolizines. The spectral properties of cationic and anionic sigma complexes involving indolizines were discussed.

Reactions of N-(4-methoxybenzylidene)-N,N-dialkyliminium and 2-(4-methoxyphenyl)pyridinium salts with aliphatic amines

The reaction of 4-methoxybenzylideneiminium salts with methylamine and dimethylamine on heating results in replacement of the MeO group by an alkylamino-group, whereas the reaction with piperidine affords 3,5-bis-(4-methoxybenzyl)pyridine. N-Methyl-2-(4-methoxyphenyl)pyridinium iodide on treatment with methylamine undergoes dealkylation to the arylpyridine.

Mass spectrometry and structure of heterocyclic ions by collisional activation.

The fragmentation of isomeric dimethylnitroindolizines due to electron impact was studied by collisional activation and high resolution mass spectroscopy. The [M-OH]+ ion which is formed as a result of the ortho-effect was found to have a variable structure. In the case of 2,8-dimethyl-1-nitroindolizine, one of the main fragmentation processes of [M-OH]+ is the elimination of an H2O molecule.

Structure and ambiphilic reactivity of indolizines. 6. Scope of the isomerizational recyclization of indolizines

The behavior of substituted 6- and 8-nitroindolizines in the isomerizational recyclization reaction has been examined. A novel method of synthesis of 2-acyl-5- and 7-nitroindoles has been developed, by recyclization of 3-acyl-6- and 8-nitroindolizines. The scope of the isomerizational recyclization of indolizines for the synthesis of indoles has been established.

Structures and ambiphilic reactivities of indolizines. 5. Acylation of 2-methylindolizine

The acylation and carbomethoxylation of 2-methylindolizine were studied. In most cases minor amounts of the 1-substituted isomers were isolated in addition to the “usual” products of substitution in the 3 position. The data from the PMR and mass spectra of the 2-methyl-3- and 1-acylindolizines obtained are discussed.

Recyclization of 6(8)-nitro-3-trifluoroacetyl-2-phenylindolizine with formation of 5(7)-nitro-3-phenylindole-2-carboxylic acid

We found that by the action of aqueous-alcoholic alkali (KOH in 50% ethanol, concentration 3 M), at room temperature, indolizines la, b readily undergo recyclization, which is accompanied by a haloformic reaction with the formation of nitroindolecarboxylic acids lla, b. We should note that compound lla is a key intermediate in the synthesis of tranquilizers nitrazepam [i] and hypnone [2]. Acylindolizine Ic, which does not contain an NO= group is deacetylated* under these conditions, forming indolizine lllc (83%).

Mass spectrometry and structures of ions of heterocyclic compounds activated by collision. 2. 2-Methylnitroindolizines

The principal pathways of the fragmentation of 2-methylnitroindolizines were investigated. The fragmentation and structures of the isomeric [M-OH]+ and [M-NO]+ ions formed in the fragmentation of these compounds were studied by the method of dissociative activation by collision (DAC). It was established that the stable [M-OH]+ ions formed in the fragmentation of the 1- and 3-nitro isomers as a result of the “ortho effect” have different structures and that their DAC spectra can be used to determine the position of the nitro group in the molecule.

Structure and ambiphilic reactivity of indolizines. 2. 8(6)-Acetyl- and cyanoindolizines

Quaternization of 2-methyl-3(5)-acetyl and cyanopyridines with α-bromoketones followed by cyclocondensation has given a number of 8(6)-acetyl- and cyanoindolizines.

Reaction of hexaalkyldisilanes with bromine and iodine

Conclusions1.The organosilicon compounds Me4Si, Et4Si, Me6Si2, and Et6Si2 form donor-acceptor complexes with Br2 and I2.2.The kinetic and activation parameters of the following reactions were determined: R6Si(R=Me, Et) with Br2 and I2 inCCl4, CH2Cl2, 1,2 C2H4Cl2.3.The halogenolysis of hexaalkyldisilanes proceeds by a molecular mechanism.

Generation of free radicals by reaction of some organotin and orga n omer cur y compounds with bromine

1. The dark bromodemetalation of a number of organotin and organomercury compounds in toluene or p-fluorotoluene initiates the free-radical bromination of the solvents in the methyl group, which testifies to the generation of free radicals during bromodemetalation. 2. A halodemetalation mechanism was proposed, which postulates that donor-acceptor complexes between the reactants, in which the organometallic compound functions as the donor and the halogen functions as the acceptor, take part in the reaction. The mechanism makes it possible to interpret the results obtained in the study (generation of radicals), as well as the previously observed generation of carbcations in the given reaction.