Lithium Organyls Research Articles

ChemInform Abstract: Selective Michael Reaction Controlled by Supersilyl Protecting Group.

AbstractSelective single and double Michael addition reactions of lithium organyls to acrylates are achieved using —Si(SiEt3)3 (supersilyl) as a carboxyl protecting group.

Chiral and achiral basket-handle porphyrins: short synthesis and stereostructures of these versatile building blocks.

Both, chiral and achiral basket-handle porphyrins were synthesized via a short, reliable, and efficient route in multigram quantities. Standard synthetic protocols such as metalation of the macrocycle, halogenation, and borylation of the porphyrin core or alkyl- and arylation with lithium organyls were successfully adapted. The planar-chiral representatives were resolved into their enantiomers, whose absolute configurations were determined by comparison of experimental CD spectra with TDCAM-B3LYP calculated ones.

ChemInform Abstract: Towards the Core Structure of Strychnos Alkaloids Using Samarium Diiodide‐Induced Reactions of Indole Derivatives.

This report describes the development of a first and second generation approach towards the synthesis of the ABCEG pentacyclic core structure of Strychnos alkaloids. First, we discuss a sequential approach applying a series of functional group transformations to prepare suitable precursors for cyclization reactions. These include attempts of samarium diiodide-induced cyclizations or a Barbier-type reaction of a transient lithium organyl, which successfully led to a tetracyclic key building block earlier used for the synthesis of strychnine. Secondly, we account our first steps towards the development of an atom-economical samarium diiodide-induced cascade reaction using dimeric indolyl ketones as cyclization precursors. In this context, we discuss plausible mechanisms for the samarium diiodide-induced cascade reaction as well as transformations of the obtained tetracyclic dihydroindoline derivatives.

Reduction of hydroxy-functionalised carbaboranyl carboxylic acids to tertiary alcohols by organolithium reagents

Reduction of hydroxy-functionalised carbaboranyl carboxylic acids by organolithium reagents yields the corresponding tertiary alcohols. This is in contrast to exo-polyhedral C-C bond cleavage of unsubstituted carbaboranyl carboxylic acids upon reaction with lithium organyls. The proposed dimeric contact ion pairs may also explain the formation of tertiary alcohols instead of the expected ketones.

Towards the Core Structure of Strychnos Alkaloids Using Samarium Diiodide‐Induced Reactions of Indole Derivatives

This report describes the development of a first and second generation approach towards the synthesis of the ABCEG pentacyclic core structure of Strychnos alkaloids. First, we discuss a sequential approach applying a series of functional group transformations to prepare suitable precursors for cyclization reactions. These include attempts of samarium diiodide-induced cyclizations or a Barbier-type reaction of a transient lithium organyl, which successfully led to a tetracyclic key building block earlier used for the synthesis of strychnine. Secondly, we account our first steps towards the development of an atom-economical samarium diiodide-induced cascade reaction using "dimeric" indolyl ketones as cyclization precursors. In this context, we discuss plausible mechanisms for the samarium diiodide-induced cascade reaction as well as transformations of the obtained tetracyclic dihydroindoline derivatives.

On the Solution Behaviour of Benzyllithium⋅(−)-Sparteine Adducts and Related Lithium Organyls - A Case Study on Applying7Li,15N{1H} HMQC and Further NMR Methods, Including Some Investigation into Asymmetric Synthesis

2D (7)Li,(15)N heteronuclear shift correlation through scalar coupling has successfully been applied to several lithium organyls consisting of polydentate N ligands such as N,N,N',N'-tetramethylethylenediamine (tmeda), N,N,N',N',N''-pentamethyldiethylentriamine (pmdta) and (-)-sparteine. Structural insights on the conformation of benzyllithium·pmdta (5) in a toluene solution and the strength of ion pairing in combination with PGSE NMR measurements, (1)H,(1)H-NOESY and (1)H,(7)Li-HOESY experiments are presented. By studying in detail the formation of 5 in solution, a transient species has been observed for the first time and assigned to a pre-complex of nBuLi and pmdta. In addition, the solution behaviour of the complex formed between benzyllithium and (-)-sparteine (8) has been studied by PGSE and multinuclear NMR spectroscopy. The straightforward synthesis and first applications in asymmetric lithiations are also reported, which show that the new system benzyllithium·(-)-sparteine (8) provide poorer enantioselective induction than the classical nBuLi·(-)-sparteine (6). The results were supported by deprotonation experiments confirming that the formation of 8 relies on two relevant factors, namely temperature and lithiating reagent. The existence of 8 may thus interfere with the asymmetric induction when the system nBuLi· (-)-sparteine is used in the enantioselective deprotonations of N-Boc-N-(p-methoxyphenyl)-benzylamine conducted in toluene.

New Syntheses and Ring Expansion Reactions of Cyclobutenimines

Two routes are reported for the synthesis of iminocyclobutenones having N-(het)aryl substitution: an addition/substitution sequence starting with cyclobutenediones and an aza-Wittig method. A new synthetic route to N-alkyl derivatives is also presented. This involves O-alkylation of 3-alkylamino-1,2-cyclobutenediones using Meerwein’s reagent and subsequent deprotonation under non-hydrolytic conditions. Lithium organyls were found to add to the remaining carbonyl group. The resulting tertiary alcohols undergo ring enlargement on heating in xylene to give 4-aminophenols, 4-amino-1-naphthols, or cyclopenta-annulated quinolines from 4-vinyl, 4-aryl, and 4-alkynyl derivatives, respectively.

Tetrahedral homonuclear organoelement clusters and subhalides of aluminium, gallium and indium.

This review is focused on the synthesis and the reactivity of tetrahedral organoelement clusters of the heavier elements of third main-group aluminium, gallium, and indium, which have been known for about a decade. They possess the elements in an unusually low oxidation state of +1 and have direct element--element interactions between their four constituents. Each cluster atom is further attached to one terminal and in most cases a bulky organic substituent, which prevents disproportionation by steric shielding. The synthesis of these compounds succeeds by different methods such as the reduction of suitable organoelement(III) halides with alkali metals and magnesium or the treatment of element(I) halides with lithium organyls. They are deeply coloured, and their bonding situation may best be described by delocalized molecular orbitals. They show a singular chemical reactivity, which results in the formation of many secondary products possessing unprecedented structures and properties. The synthesis of organoelement subhalides still containing the elements in low oxidation states is discussed in more detail in the second part of this review. These compounds are easily accessible by the careful oxidation of the clusters with halogen donors such as hexachloroethane or with AlX(3)/X(2) mixtures. They produce dimers via halogen bridges, but in certain cases monomers were observed even for the solid state. They are very effective starting compounds for secondary reactions and the generation of new products containing the elements in unusual oxidation states by salt-elimination reactions, for instance.

A multidentate phosphinoalkoxide ligand as a building block in mixed polylithium aggregates

The tris(dimethylphosphinomethyl)-substituted lithium alkoxide [LiOC(CH2PMe2)3] acts as a building block in mixed polylithium aggregates, effectively capping triangular Li3 polyhedral faces; it further reacts with lithium organyls to yield the Y-conjugated, symmetrically tris(dimethylphosphino)-substituted trimethylenemethane dianion.

Ladder Structure of a Lithium Organyl: Synthesis and Crystal Structure of a Mixed Aggregate of n-BuLi and an (Aminomethyl)(lithiomethyl)silane

A mixture of n-BuLi and the (aminomethyl)(lithiomethyl)silane 3 shows a higher reactivity than the separate compounds. A single-crystal X-ray structure of the mixed aggregate between n-BuLi and the (lithiomethyl)silane ([3·n-BuLi]2) establishes a ladder structure of the lithiumorganyl in the solid state.

Addukte der Ethene Me 2EC(SiMe 3) 2 (E=Si, Ge, Sn) mit LiR und RN 3: Wie rasch bilden sie sich?

Unsaturated compounds Me 2EC(SiMe 3) 2 (E=Si, Ge, Sn) are formed as short-lived intermediates by reaction of Me 2EXCBr(SiMe 3) 2 with LiR via Me 2EXCLi(SiMe 3) 2 (X=electronegative substituent; R=organyl) and — in the absence of trapping reagents — react with Me 2EXCLi(SiMe 3) 2 and LiR (as long as present) under formation of cyclobutanes [Me 2EC(SiMe 3) 2] 2 as well as adducts Me 2ERCLi(SiMe 3) 2 of Me 2EC(SiMe 3) 2 and LiR. In the presence of an excess of organyl or silyl azides RN 3, as well as lithium organyls or silyls LiR, which indeed act as very active trapping reagents for Me 2EC(SiMe 3) 2 with formation of [3+2] cycloadducts Me 2EC(SiMe 3) 2 ·RN 3 and adducts Me 2ERCLi(SiMe 3) 2, the formation of cyclobutanes and adducts is suppressed in the first case, whereas adducts are formed exclusively in the second case. As a result of determination of relative amounts of the products, formed by addition of Me 2SiBrCBr(SiMe 3) 2 to two different trapping reagents LiR and LiR′ or LiR and RN 3 in Et 2O, relative rates of the reactions of LiR or RN 3 with the silene Me 2SiC(SiMe 3) 2 are determined. Hereafter the insertion reactivity of LiR and the [3+2] cycloaddition reactivity of RN 3 decreases when the bulkiness of R increases (decreasing reactivity in the order LiMe>Li n Bu>LiPh>Li t Bu; LiMe>LiCH(SiMe 3) 2>LiC(SiMe 3) 3; Me 3SiN 3> t BuMe 2SiN 3> t Bu 2HSiN 3> t Bu 2MeSiN 3>Ph 3SiN 3> t Bu 3SiN 3). The influences of electronic effects are obviously smaller than those of steric effects (decreasing reactivity in the order LiC(SiClMe 2)(SiMe 3) 2>LiC(SiBrMe 2)(SiMe 3) 2>LiC(SiMe 3) 3; t Bu 2MeSiN 3> t Bu 2ClSiN 3; Me 3CN 3>Me 3SiN 3).

Comparison on the selectivity of the first and second attack of selected lithium organyls as nucleophiles on the carbonyls in the bioctahedron complexes M 2( μ-PPh 2) 2(CO) 8 (M=Mn, Re). Is there a neighbour group effect for the second attack?

In thf solution the bioctahedron complex Re 2( μ-PPh 2) 2(CO) 8 1 reacts with one equiv of LiR (R=Ph, Me, nBu, tBu) at temperatures between −90 and −50°C to the acyl monoanion Li[Re 2( μ-PPh 2) 2(CO) 7(ax-C(R)O)] 3 and with a second equiv of LiR 1 (R 1=Ph, Me, nBu) at 20°C to the diacyl dianions Li 2[Re 2( μ-PPh 2) 2(CO) 6(ax-C(R)O)(ax-C(R 1)O)] 12 as trans or cis isomers. Both nearly quantitative reaction steps run selectively: First, both lithium nucleophiles attack exclusively axially coordinated carbonyl ligand. Second, the monoanion with R=Ph forms exclusively the cis diacyl dianions (R 1= nBu, Ph). Through this reaction an anchimeric effect was proved. Third, the monoanions with R= nBu, Me react only to the trans diacyl dianions. In general such mono- and dianions have been reacted with O-alkylating agens to the corresponding carbene and dicarbene derivatives (yield 50–70%) to get single crystals for X-ray structure analyses. All products were identified by means of 1H, 1P NMR and ν(CO)IR data. Additionally the molecular structures of the Fischer type carbene complexes Re 2( μ-PPh 2) 2(CO) 7(ax-C( tBu)OMe) 5b, cis-Re 2( μ-PPh 2) 2(CO) 6(ax-C(Ph)OEt) 2 14 and trans-Re 2( μ-PPh 2) 2(CO) 6(ax-C( nBu)OMe)(ax-C(Ph)OMe) 15b are presented. Opposite to 1 affords the homologous dimanganese complex 2 under the same reaction conditions at −50°C with one and two equiv of lithium organyl an unselective nucleophilic addition to axially and equatorially coordinated monoacyl monoanions and diacyl dianions. Our attempts to separate such isomers of the mono- and dianion type as lithium salt led to their decomposition. However, the carbene and dicarbene derivatives Mn 2( μ-PPh 2) 2(CO) 7(ax-C(Ph)OEt) 9ax and trans-Mn 2( μ-PPh 2) 2(CO) 6(ax-C( nBu)OEt) 2 16 could be crystallized as air-stable, yellow solids. Their molecular structures are presented.

Titanium Complexes with a Linked Amido−Cyclopentadienyl Ligand and a Bidentate Organyl Group: Synthesis, Structure, and Ethene Polymerization Activity

Titanium complexes containing a linked isopropyl- or benzylamido(tetramethylcyclopentadienyl) ligand C5Me4SiMe2NR (R = iPr, CH2Ph,) and one bidentate organyl group C6H4(CH2NMe2)-2, CH2C6H4(NMe2)-2, and {η5-C5H3(CH2NMe2)-2}Fe(η5-C5H5) were prepared by salt metathesis of the corresponding dichloro complex Ti(η5:η1-C5Me4SiMe2NR)Cl2 with the lithium organyl. Single crystal X-ray structural analysis of Ti(η5:η1-C5Me4SiMe2NCH2Ph)- {C6H4(CH2NMe2)-2}Cl and of Ti(η5:η1-C5Me4SiMe2NiPr){CH2C6H4(NMe2)-2}Cl revealed the presence of intramolecular coordination with square pyramidal geometry around titanium. In the ferrocenyl derivative Ti(η5:η1-C5Me4SiMe2NCH2Ph)[{η5-C5H3(CH2NMe2)-2}Fe(η5-C5H5)]Cl the NMe2 group is not bonded at the titanium atom. Ethene polymerization catalyzed by these complexes upon activation with methylaluminoxane was examined.

Titanium Complexes with a Linked Amido−Cyclopentadienyl Ligand and a Bidentate Organyl Group: Synthesis, Structure, and Ethene Polymerization Activity

Titanium complexes containing a linked isopropyl- or benzylamido(tetramethylcyclopentadienyl) ligand C5Me4SiMe2NR (R = iPr, CH2Ph,) and one bidentate organyl group C6H4(CH2NMe2)-2, CH2C6H4(NMe2)-2, and {η5-C5H3(CH2NMe2)-2}Fe(η5-C5H5) were prepared by salt metathesis of the corresponding dichloro complex Ti(η5:η1-C5Me4SiMe2NR)Cl2 with the lithium organyl. Single crystal X-ray structural analysis of Ti(η5:η1-C5Me4SiMe2NCH2Ph)- {C6H4(CH2NMe2)-2}Cl and of Ti(η5:η1-C5Me4SiMe2NiPr){CH2C6H4(NMe2)-2}Cl revealed the presence of intramolecular coordination with square pyramidal geometry around titanium. In the ferrocenyl derivative Ti(η5:η1-C5Me4SiMe2NCH2Ph)[{η5-C5H3(CH2NMe2)-2}Fe(η5-C5H5)]Cl the NMe2 group is not bonded at the titanium atom. Ethene polymerization catalyzed by these complexes upon activation with methylaluminoxane was examined.

Erzeugung, nachweis und stabilisierung isomerer silaethene R 2Si [dbnd]C(SiR 3) 2 mit jeweils sechs Me- und zwei Ph-substituenten R

Bromotrisilylmethanes Me 2SiBr CBrRR 2 ( 2b), PhMeSiBr CBrRR 1 ( 3b, two diastereomers) and Me 2SiBr CBrR 2 1 ( 4b) (R SiMe 3, R 1 SiMe 2Ph, R 2 SiMePh 2) - sources of silaethenes Me 2Si CRR 2 ( 2), PhMeSi CRR 1 ( 3, two isomers), and Me 2Si CR 2 2 ( 4) - are formed by bromination of Me 2SiH CBrRR 2 ( 2a), PhMeSiH CBrRR 1 ( 3a, two diastereomers; bromination takes place stereospecifically), and Me 2SiH CBrR 2 2 ( 4a), which themselves are formed from CBr 4 by introducing three silyl groups step by step according to: ≤Cz.sbnd;Br+R′Li+≤SiCl→≤C Si≤+R′Br+LiCl(R′ = ″Bu, (Me 3Si) 2CH). The structure of one of the two diastereomeric compounds, 3a, has been solved by X-ray analysis. PhLi converts 2b–4b by Br/Li-exchange to lithium organyls Me 2SiBr CLiRR 2 ( 2c). PhMeSiBr CLiRR 1 ( 3b, two diastereomers), and Me 2SiBr CLiR 2 1 ( 4c), which in Et 2O at −78°C are in equilibrium with silaethenes 2, 3 and 4 in very low concentrations. The intermediacy of the silaethenes has been established chemically by trapping 2, 3 and 4 with 2,3-dimethyl-1,3-butadiene (DMB): formation of[4 + 2] cycloadducts 2d, 3d (two diastereomers) and 4d, of ene reaction products 2e, 3e (two diastereomers), and 4e as well as of[4 + 2] cycloadducts 2f (diastereomers), 3f (diastereomers), and 4f of the formed ene reaction products. The structure of one of the two diastereomeric compounds, 3d, has been solved by X-ray analysis. By warming the etheral solutions of 2c, 3c and 4c,[2 + 2] cycloadducts 2 × 2, 2 × 4 and 4 × 4 of silaethenes 2 and 4 are found. Considering the types and yields of the products of silaethenes - including Ph 2Si CR 2 ( 1) - in the absence and the presence of DMB, the following is concluded; (i) silaethenes 1, 2, 3, 4 are in equilibrium by methyl and phenyl group migrations; (ii) the relative thermodynamic silaethene stability increases in the order 1 < 3 < 4 < 4 (phenyl groups at unsaturated silicon destabilize the silaethenes as a consequence of electronic effects of phenyl; (iii) silaethenes 1–4 are kinetically more stable against [2 + 2] cycloadditions than silaethene Me 2Si C(SiMe 3) 2 (as a consequence of steric effects of phenyl); (iv) the rate of methyl and phenyl group migration is equal; (v) substitution of methyl groups at unsaturated silicon (saturated silicons) in Me 2Si C(SiMe 3) 2 increases (does not increase) the SiC double bond polarity.

1,4-Addition of Lithium Organyls to para-Quinols / Structure Determination of 2,6-Di-tert-butyl-4-hydroxy-4,5-diphenylcyclohex-2-en-1-one

Abstract Addition of lithium organyls to sterically hindered para-quinols leads to 1,2-or 1,4-adducts. The 1,4-addition prevails, if the 4-substituents in the quinol and the organic group in the lithium organyl are large. Four 1,4-addition products (2-cyclohex-2-en-1-ones) are synthesized and their structures investigated by NMR spectroscopy. The aryl groups at C-4 and C-5 acquire equatorial positions, the alkyl group at C-6 is bisectional. These results are confirmed by X-ray analysis of 2,6-di-tert-butyl-4-hydroxy-4,5-diphenylcyclohex-2-en-1 -one, revealing a twist boat conformation of the cyclohexene ring.

Asymmetric Synthesis via Heterocyclic Intermediates, LII. Synthesis of tert‐Leucine and Related Amino Acids

AbstractThe 2,5‐dialkoxypyrazines 3a and b were prepared in three steps from methyl glycinate hydrochloride (1) in an overall yield of 18 and 63%. Upon the addition of lithium organyls to 3b and subsequent acidic hydrolysis the ethyl glycinates rac‐7 were obtained.

ChemInform Abstract: Reaction of Thienyltitanocene Chloride with Organo‐Lithium Compounds.

AbstractThe thienyltitanocene chloride (I) reacts with the lithium organyls (II) to give the titanocenes (III), containing two different σ‐bound substituents at the titanium atom.

ChemInform Abstract: Chemistry of Boron. Part 179. Synthesis, Conformation, and Molecular Structure of Sterically Crowded Aminomethyleneborane Precursors.

AbstractReaction of the piperidinoboron dihalides (I) with the lithium organyls (II) gives the boranes (III); only in the case of the reaction between (Ia) and (IIa) is the para‐phenyl substituted borane (IV) obtained.

ChemInform Abstract: Nucleophilic Substitution at the Biocoordinated Phosphorus Atom in P‐(Amino)methylenephosphines.

AbstractThe methylenephosphine (I) reacts with the lithium organyls (II) to give the corresponding phosphines (III) by nucleophilic substitution of the bistrimethylsilylamino group.