Stereoselective synthesis of 2-alkylidene-3-iminoindoles by reaction of 1,1-dianions with oxalic acid bis(imidoyl) chlorides

Identification of the monoanions and of their complexes with lithium salts possibly formed in solution during the alkylation of lithiated phenylacetonitrile dianions: infrared spectroscopy and density functional theory calculations

The carbanionic species possibly formed during the first alkylation step of phenylacetonitrile lithiated anion by CH(3)I and PhCH(2)Cl in THF-hexane solution and their complexes with the lithium salt formed have been observed by infrared spectrometry and characterized by density functional theory calculations. The spectra of alkylated phenylacetonitrile lithiated anion monomers and dimers have been identified in good agreement with calculations. The wave numbers of the vibrational modes of the alkylated species differ significantly from those of PhCHCNLi species, but do not depend appreciably on the substituent nature. Nevertheless with the methyl substituent, the isomerization equilibrium of the monomer is noticeably shifted toward the bridged (C-lithiated) species. The formation of a heterodimer at the expense of the dimer after addition of LiCl has been confirmed by experiment.

Study of the lithiated phenylacetonitrile monoanions and dianions formed according to the lithiated base used (LHMDS, LDA, or n-BuLi). 1. Evidence of heterodimer ("Quadac") or dianion formation by vibrational spectroscopy

It is evidenced through vibrational spectroscopy that a heterodimer or "Quadac" is formed when an excess of base (LHMDS, LDA, or n-BuLi) is added to PhCH(2)CN in THF, THF-hexane, or THF-toluene solution. The amount of heterodimer increases with the pK(H)(a) of the lithiated base. A dianionic species may be formed through decomposition of this heterodimer if the pK(H)(a) of the base is sufficiently high, as in the case of n-BuLi. With LDA, only a very small amount of dianion is observed, and with LHMDS, no dianion is detected. The predominant dianionic species observed are the linear and bridged separated ion pairs of the dilithiated dianion. The presence of the amine in the medium is of paramount importance. The PhCHCNLi monomer-dimer equilibrium is entropy driven toward the dimer solvated by the amine.

Structural and vibrational characterization of the mono and dilithiated species derived from phenylacetonitrile in THF by infrared and Raman spectroscopy and density functional theory calculations

The structures and spectra of mono and dianionic species derived from PhCH2CN under the action of an organic base LHMDS or n-BuLi in THF solution have been investigated by vibrational spectroscopy and DFT calculations. The assignments previously proposed for the monoanion, the bridged, linear and dimeric monoanionic ion pairs compare well with the calculated ones. The addition of HMPA to a THF solution of PhCHCNLi leads to the formation of an HMPA solvated linear ion pair, distinguishable from the bridged ion pair by the wave number of the 8a v(CC) phenyl ring mode. The calculated structure of the phenylacetonitrile anion in the (PhCHCNLi, CH3Li) mixed dimer or 'Quadac' is very similar to that in the linear ion pair or in the dimer and to that observed by X-ray in (PhCHCNLi, [CH(CH9)2]2NLi) 'Quadac'. The structure of the anion is planar, indicating a charge delocalization from the benzene ring to the -CHCN group. The calculated spectra of the free, mono and dilithiated dianionic species compare well with the experimental ones of the species formed under addition of more than one equivalent of n-BuLi. The structure of the >C-C-CN2- group is very close to that of an imine. The v(CN) bands of the free, mono and dilithiated dianionic species are located at 1912, 1930 and 1890 cm(-1), respectively. The large wave number shift observed between the free monoanion and dianion (approximately 176 cm(-1)), in good accordance with the calculated one (170 cm(-1)) allows differentiating mono and dianionic species. The shifts observed for the 8a and 19a v(CC) phenyl ring modes, although much smaller, also allows discriminating the different species. These small shifts indicate a small variation of the electronic delocalization in the benzene ring in agreement with the calculations.

Efficient and stereoselective synthesis of bicyclo[3.2.1]octan-8-ones: synthesis and palladium-catalyzed isomerization of functionalized 2-vinyl-2,3,3a,4,5,6-hexahydro-2,3-benzofurans

A new C,O-cyclodialkylation of dilithiated cyclic beta-keto esters and beta-keto sulfones with 1,4-dibromo-2-butene is reported which results in regio- and diastereoselective formation of 2-vinyl-2,3,3a,4,5,6-hexahydro-2,3-benzofurans. The products could be efficiently transformed into functionalized bicyclo[3.2.1]octan-8-ones by a palladium-catalyzed rearrangement reaction. In case of sulfone derivatives, this rearrangement proceeds with high stereospecifity to give exclusively the endo-configured diastereomers. The bicyclo[3.2.1]octane skeleton is present in a large number of pharmacologically important natural products.

Chemo-, regio-, and diastereoselective synthesis of functionalized cyclopropanes by cyclization of dilithiated nitriles with epibromohydrin

The cyclization of 1,1-dianions with epibromohydrin results in chemo-, regio-, and diastereoselective formation of functionalized hydroxymethyl cyclopropanes. [reaction: see text]

Regio- and diastereoselective cyclization reactions of free and masked 1,3-dicarbonyl dianions with 1,2-dielectrophiles

Despite their simplicity and synthetic usefulness, cyclisation reactions of 1,3-dicarbonyl dianions with 1,2-dielectrophiles are problematic, since both dianions and 1,2-dielectrophiles are highly reactive compounds (low reactivity matching). In addition, 1,2-dielectrophiles are often rather labile, and reactions with nucleophiles can result in polymerisation, decomposition, formation of open-chained products, elimination or SET-reactions. These intrinsic limitations can be overcome by a proper reactivity tuning and by the use of electroneutral dianion equivalents (masked dianions) in Lewis acid catalysed reactions. The cyclisations reported herein allow for an efficient, regio- and stereoselective one-pot synthesis of biologically relevant ring systems.

Regio- and stereoselective synthesis of Nor-nonactinic acid derivatives--kinetic reaction control in the Lewis acid mediated domino reaction of 1,3-dicarbonyl dianions with 1-bromo-2,3-epoxypropanes

Reaction of 1,3-dicarbonyl dianions with epibromohydrin derivatives results in formation of functionalized 2-alkylidene-5-hydroxymethyltetrahydrofurans. These reactions proceed by chemoselective attack of the dianion onto the carbon attached to the bromine atom and subsequent nucleophilic attack of the resultant monoanion onto the epoxide. The cyclization products, which were formed with very good regio- and stereoselectivities, are of pharmacological relevance and represent versatile building blocks for the synthesis of natural products.