Lithium Naphthalenide Research Articles

Polymerization of 1,3-Dienes with Functional Groups. 4.

Anionic polymerization of N,N-diethyl-2-methylene-3-butenamide (DEA), which is a 1,3-butadiene derivative containing a diethylamide function, was carried out in tetrahydrofurane (THF) under various conditions. When DEA was polymerized in THF at −78°C using potassium naphthalenide (K-Naph) or diphenylmethylpotassium (DPMK) as an initiator, a polymer of predictable molecular weight with a narrow molecular weight distribution was obtained. However, the rate of polymerization was extremely slow to reach 80% conversion after 720 h. When the polymerization temperature was raised to 20°C, a low molecular weight oligomer with a broad molecular weight distribution was obtained because of a chain transfer reaction. On the other hand, no such side reaction occurred even at 20°C, when polymerization was carried out in the presence of LiCl. Also, the chain transfer reaction did not occur in lithium naphthalenide (Li-Naph) initiated polymerization. The microstructure of the polymer prepared using a potassium counter cation was a 1 : 1 mixture of 1,4-E and 1,2- structures. In the case of Li-Naph or DPMK/LiCl systems, the microstructure was a complicated mixture of 1,4-E, 1,4-Z, and 1,2-structures.

Efficient Preparation of α,α-Dialkyl-α-(phenylselanyl)acetates and α,β-Unsaturated Esters from the Corresponding α,α-Dialkyl-α-cyanoacetates by a Lithium Naphthalenide Induced Reductive Selenenylation Process

An array of α,α-dialkyl-α-(phenylselanyl)acetates has been synthesized very efficiently from readily available α,α-dialkyl-α-cyanoacetates, by use of lithium naphthalenide induced reductive α-selenenylation as a key operation. Moreover, the selanyl esters thus generated in situ could be converted further, in a one-pot treatment with hydrogen peroxide and acetic acid, into the corresponding α,β-unsaturated esters in moderate to high yields. The C=C bond formation was highly regio- and/or diastereoselective in some cases.

Lithium Naphthalenide Induced Reductive Selenenylation of α-Cyano Ketones: A Regiocontrolled Process for α-Phenylseleno Ketones and One-Pot Conversion into Enone System

An efficient procedure for the regiocontrolled synthesis of α-phenylseleno ketones has been developed, making use of the lithium naphthalenide induced reductive selenenylation of the α-cyano ketone system as a key operation. Moreover, seleno ketones thus generated in situ, upon subsequent treatment with hydrogen peroxide and acetic acid, could be further converted into the corresponding enones with a high degree of regioselectivity, presumably due to the lithium salt mediated selenoxide syn-elimination process.

Boryllithium: Isolation, Characterization, and Reactivity as a Boryl Anion

Nucleophilic, anionic boryl compounds are long-sought but elusive species. We report that reductive cleavage of the boron-bromine bond in N,N'-bis(2,6-diisopropylphenyl)-2-bromo-2,3-dihydro-1H-1,3,2-diazaborole by lithium naphthalenide afforded the corresponding boryllithium, which is isoelectronic with an N-heterocyclic carbene. The structure of the boryllithium determined by x-ray crystallography was consistent with sp(2) boron hybridization and revealed a boron-lithium bond length of 2.291 +/- 0.006 angstroms. The structural similarity between this compound and the calculated free boryl anion suggests that the boron atom has an anionic charge. The (11)B nuclear magnetic resonance spectrum also supports the boryl anion character. Moreover, the compound behaves as an efficient base and nucleophile in its reactions with electrophiles such as water, methyl trifluoromethanesulfonate, 1-chlorobutane, and benzaldehyde.

The Chemistry of Silicon‐Containing Ladder π‐Conjugated Systems

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General Method for Synthesizing Pyranoid Glycals. A New Route to Allal and Gulal Derivatives

[reaction: see text] Pyranoid glycals of all configurations can be obtained from pentoses through an olefination-cyclization-elimination sequence. The elimination can be carried out with excellent yields under radical conditions or by using common reductive reagents such as Zn/Cu, TiCl(4)/LiAlH(4), or lithium naphthalenide. The proposed method is appropriate for the synthesis of glycals with allo or gulo configurations because the cyclization step is more efficient for these substrates.

Reductive Ring Opening of Dihydrodibenzothiepine and Dihydrodinaphtho‐oxepine and ‐thiepine.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Generation and Reactions of Overcrowded Diaryldilithiostannane and Diaryldipotassiostannane

AbstractExhaustive reduction of an overcrowded dibromostannane bearing two bulky aromatic substituents, Tbt(Dip)SnBr2 {Tbt = 2,4,6‐tris[bis(trimethylsilyl)methyl]phenyl; Dip = 2,6‐diisopropylphenyl}, with an excess amount of lithium naphthalenide in THF at –78 °C gave the corresponding dilithiostannane, Tbt(Dip)SnLi2, the generation of which was confirmed by trapping experiments with some electrophiles together with 119Sn and 7Li NMR spectroscopy. The diaryldilithiostannane was found to be stable in solution under an inert gas below –25 °C. The potassium analogue, Tbt(Dip)SnK2, was also generated by the reduction of the dibromostannane in THF at –78 °C by the use of KC8 as a reductant. The reactions of dilithiostannane and dipotassiostannane obtained with o‐dibromobenzene did not give a stannacyclopropabenzene derivative but an unexpected cyclization product, a stannacyclobutabenzene derivative, in contrast to thereactions of the corresponding dilithiosilane and dilithiogermane, Tbt(Dip)ELi2 (E = Si, Ge), with o‐dibromobenzene leading to the formation of the corresponding metallacyclopropabenzenes as stable crystalline compounds. A preliminary result of the synthesis of a tin–tellurium double‐bond compound from the dilithiostannane is also presented. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Reductive ring opening of dihydrodibenzothiepine and dihydrodinaphtho-oxepine and -thiepine

The 4,4′di- tert-butylbiphenyl (DTBB)-catalysed lithiation of dihydrodibenzothiepine ( 1 ) at −78 °C for 30 min followed by reaction with a carbonyl compound [ t BuCHO, Ph(CH 2) 2CHO, PhCHO, ( n-C 5H 11) 2CO, (CH 2) 5CO, (CH 2) 7CO, (−)-menthone] at the same temperature leads, after hydrolysis with 3 M hydrochloric acid, to sulphanyl alcohols 2 . If after addition of a carbonyl compound as the first electrophile [Me 2CO, (CH 2) 5CO, (−)-menthone], the resulting dianion of type II is allowed to react at room temperature for 30 min, a second lithiation takes place to give an intermediate of type III , which by reaction with a second electrophile [Me 2CO, Et 2CO, (CH 2) 5CO, ClCO 2Et], yields, after hydrolysis, difunctionalised byphenyls 4 . The cyclisation of the sulphanyl alcohol 2c under acidic conditions yields the eight-membered sulphur containing heterocycle 3 . The lithiation of dihydrodinaphthoheteroepines 7 and 10 with 2.2 equiv of lithium naphthalenide in THF at −78 °C followed by reaction with different electrophiles [H 2O, D 2O, t BuCHO, Me 2CO, Et 2CO, (CH 2) 4CO, (CH 2) 5CO] at the same temperature leads, after hydrolysis, to unsymmetrically 2,2′-disubstituted binaphthyls 9 and 12 , respectively. When the lithiation is performed with an excess of lithium in the presence of a catalytic amount of DTBB (10% molar), a double reductive cleavage takes place to give the dianionic intermediate VII , which by reaction with different electrophiles [H 2O, Me 2CO, Et 2CO, (CH 2) 4CO, (CH 2) 5CO], followed by hydrolysis with water, yields symmetrically 2,2′-disubstituted binaphthyls 8 and 11 . In the case of starting from ( R)- or ( S)-dihydrodinaphthoheteroepines 7 and 10 , these methodologies allow us to prepare enantiomerically pure compounds 8 , 11 and 12 .

Synthesis, structures, and photophysical properties of silicon and carbon-bridged ladder oligo( p-phenylenevinylene)s and related π-electron systems

A series of partially or fully fused ladder oligo( p-phenylenevinylene)s (LOPVs) and related π-electron systems has been synthesized. Thus, the intramolecular reductive cyclization of o-silyl-substituted bis(phenylethynyl)benzenes with lithium naphthalenide produces partially silicon-bridged bis(styryl)benzenes consisting of silaindene or disilaindacene skeletons. By combining this cyclization with the Friedel–Crafts type electrophilic cyclization, a homologous series of the fully fused LOPVs and related compounds, bearing silicon and carbon bridges, has been synthesized in fairly good yields. The longest example of the LOPVs is the 13-ring-fused system that has a nearly flat π-conjugated framework with a length of 2.9 nm, as proven by X-ray crystallography. All the produced ladder π-electron systems show intense fluorescence in the visible region with high quantum yields as well as relatively small Stokes shifts. As the silicon contents increase or the disilaindacene skeleton is incorporated, the emission maxima shift to the longer wavelengths and the fluorescent quantum yields slightly decrease. These trends can be rationalized as due to the σ* effect of silicon, wherein the silicon bridges contribute to the electronic structure through σ*–π* orbital interaction that cause the red-shifts in the emission maxima and suppress the radiative decay process from the singlet excited state.

Formation of the Dianion and the Dimer of 9,10-Distannaanthracene

Abstract The reaction of 9,10-diiodo-9,10-dihydro-9,10-distannaanthracene with lithium naphthalenide (2.5 equiv.) or excess lithium gave the 9,10-distannaanthracene dimer or the 9,10-distannaanthracene dianion. The formation of the latter was evidenced by NMR spectral analysis and a trapping experiment.

Functional Group Transformations and Stereochemistry of Silicon-functionalized 7-Silabenzonorbornadienes

Abstract Functional group transformations of 7-silabenzonorbornadiene derivatives have been investigated. The 7-mesityl-7-silanorbornadiene 1 was prepared and converted into the 7-chloro derivative 5. Reductive lithiation of 5 with lithium naphthalenide afforded the silyllithium 6, which reacted with Me3SiCl and MeI. The reactions of 5 with n-BuLi and PhNHLi gave the 7-butyl derivative 9 and the 7-amino derivative 10, respectively. Each stereochemistry during these transformations was determined by X-ray crystallographic analysis.

Diasteroselective Synthesis of New Spiropiperidine Scaffolds from the CN(R,S) Building Block

A methodology allowing the construction of spiropiperidine scaffolds similar to those found in naturally occurring alkaloids has been developed. This approach begins with the well-established CN(R,S) strategy, the spiro-center being built by way of an intramolecular attack of a nitrile function by an organolithium species obtained by a halogen/lithium exchange reaction mediated by either t-BuLi or lithium naphthalenide.

C(6)‐Alkylation of 3‐Hydroxypiperidine via Reductive and Homolytic Cleavage of N,S‐Acetals.

AbstractFor Abstract see ChemInform Abstract in Full Text.

The Chemistry of Silicon-Containing Ladder .PI.-Conjugated Systems

The intramolecular reductive cyclization of bis (ο-silylphenyl) acetylenes with lithium naphthalenide produces bis-silicon-bridged stilbenes. Based on this new cyclization, a series of silicon-bridged ladder π-conjugated systems consisting of the p-phenylenevinylene framework have been synthesized, including the partially or fully silicon-bridged bis (styryl) benzenes, extended ladder oligo (p-phenylenevinylene) s, and bis-silicon-bridged stilbene-based π-conjugated polymers. All the ladder π-electron systems show intense fluorescence in the visible region. The detailed elucidation of their photophysical properties revealed the significant effect of the silicon moieties on the fluorescence properties.

Bis-, Tris- and Tetrakis(lithiomethyl)germanes: New Building Blocks for Organogermanium Compounds

Abstract Bis(lithiomethyl)germanes, R2Ge(CH2Li)2, tris(lithiomethyl)germanes, RGe(CH2Li)3, and tetrakis( lithiomethyl)germane, Ge(CH2Li)4, were prepared by the reductive C-S bond cleavage with lithium naphthalenide (LiC10H8) or lithium p,p’-di-tert-butylbiphenylide (LiDBB) and characterized by trapping with Bu3SnCl. The bis(lithiomethyl)germanes were used for the synthesis of 1,1-dimethyl-3,3-diphenyl-1-germa-3-silacyclobutane, 1,1-diethyl-3,3-diphenyl-1-germa-3-silacyclobutane, 1,1,3,3-tetraphenyl-1-germa-3-silacyclobutane and 1,1,3,3-tetraphenyl-1,3-digermacyclobutane. The single-crystal X-ray diffraction studies of methyltris(phenylthiomethyl)germane and tetrakis(phenylthiomethyl)germane, starting materials for the corresponding poly(lithiomethyl) germanes, indicate tetrahedrally arranged substituents at the germanium atoms.

Reductive opening of 2,7-dihydrodinaphthoxepine and thiepine: easy regioselective preparation of 2,2′-difunctionalised binaphthyls

The lithiation of 2,7-dihydrodinaphthoheteroepines ( 5 ) with 2.2 equiv of lithium naphthalenide in THF at −78 °C gives dianionic intermediates 8 , which by reaction with different electrophiles [H 2O, D 2O, t BuCHO, Me 2CO, Et 2CO, (CH 2) 4CO, (CH 2) 5CO] at the same temperature, followed by hydrolysis, leads to unsymmetrically 2,2′-disubstituted binaphthyls 6 . When the lithiation is performed with an excess of lithium in the presence of a catalytic amount of 4,4′-di- tert-butylbiphenyl (DTBB, 10 mol %), a double reductive cleavage takes place to give dianionic intermediate 9 , which by reaction with different electrophiles [H 2O, Me 2CO, Et 2CO, (CH 2) 4CO, (CH 2) 5CO], followed by hydrolysis with water, yields symmetrically 2,2′-disubstituted binaphthyls 7 . In the case of starting from ( R)- 5a , the reductive opening by treatment with 2.2 equiv of lithium naphthalenide followed by reaction with H 2O or (CH 2) 5CO as electrophiles and final hydrolysis, leads to enantiomerically pure compounds ( R)- 6aa and ( R)- 6af , respectively.

C(6)-Alkylation of 3-Hydroxypiperidine via Reductive and Homolytic Cleavage of N,S-Acetals

N-Carboxymethyl 3-hydroxypiperidine (6) undergoes substitution at C(6) via reductive cleavage of N,S-acetal 8a with lithium naphthalenide (LN) and trapping of the resulting carbanionic intermediate 9 with different electrophiles to give adducts 10. N,S-Acetal 8a also undergoes C-S homolysis and trapping of the resulting radical provides an alternative entry to 2-substituted-5-­hydroxypiperidines.

General silaindene synthesis based on intramolecular reductive cyclization toward new fluorescent silicon-containing pi-electron materials.

[reaction: see text] The reaction of (o-silylphenyl)acetylene derivatives with lithium naphthalenide undergoes intramolecular reductive cyclization to produce various silaindene derivatives. On the basis of this methodology, a series of silaindene-containing pi-electron systems are synthesized that show intense blue to greenish-blue fluorescence.

Preparation of lithium stannide mixtures in organic solvents. A alternate source of lithium in organolithium chemistry

Lithium stannides were prepared from lithium naphthalenide and tin (II) chloride or tin (0) powder in THF solvent at room temperature under dry argon atmosphere. They were characterized with elemental analysis, XRD, and solid 6,7Li NMR. Stabilities and reactivities of lithium stannides prepared from different conditions were tested and showed they were stable for a limited time at low temperatures. Best reactivity was obtained when they were prepared from tin (II) chloride and an excess of lithium naphthalenide. The lithium stannide mixture can reductively cleave carbon–halogen bonds and yield pinacol coupling with aldehydes. Organolithium compounds prepared from lithium stannides and organic halides add to ketones or aldehydes under Barbier conditions.