Accurate measurement of effective Li-Li scalar coupling constants: the NMR missing link for alkyllithium aggregates.

Scalar coupling in organolithium systems can provide access to useful structural and dynamic informations. In this work, we propose a robust method for the accurate measurement of the effective 2JLi-Li coupling constant in tetramerics alkyllithium aggregates. This crucial information, unavalaible to date, gives a simple access to various structural factors, including the dynamics, solvation and the operative steric hindrance of alkyl chains.

Total synthesis of spiromastilactone A.

The total synthesis of spiromastilactone A is reported for the first time. A swift strategy is presented that involves a pivotal enantioselective nucleophilic 1,2-alkylation of an aldehyde prepared in four quantitative synthetic steps from commercial 2,4-dihydroxybenzoic acid. This key reaction, which was described very recently by our group and carried out here on a gram scale, involves cheap and easily accessible tricoordinated chiral lithium amido zincates. The resulting enantioenriched secondary alcohol is involved afterward in an efficient intramolecular cyclization providing the phthalide core of the target, and two quantitative additional steps aiming to deprotect the phenol groups then introduce chlorine atoms end the synthetic scheme. Spiromastilactone A is obtained in 44% overall yield in eight synthetic steps, among which six are quantitative, and the 89 : 11 enantiomeric ratio (78% ee value) is in favor of the right enantiomer (R configuration).

Chiral Lithium Amido Aryl Zincates: Simple and Efficient Chemo- and Enantio-Selective Aryl Transfer Reagents.

An enantioselective aryl transfer is promoted using chiral tricoordinated lithium amido aryl zincates that are easily accessible reagents and whose chiral appendage is simply recovered for reuse. The arylation reaction is run in good yields (60 % average on twenty substrates) and high enantiomeric excesses (95 % ee average). This occurs whatever the ortho, meta, or para substituent borne by the substrate and a complete chemoselectivity is observed with respect to the aldehyde function. Sensitive groups such as nitriles, esters, ketones, and enolisable substrates resist to the action of the ate reagent, warranting a large scope to this methodology.

Access to Anti or Syn 2-Amino-1,3-diol Scaffolds from a Common Decarboxylative Aldol Adduct.

A straightforward synthetic pathway allowing the access to anti or syn 2-amino-1,3-diol scaffolds is presented. The strategy relies on a diastereoselective organocatalyzed decarboxylative aldol reaction of a N-Boc-hemimalonate that is easily formed from commercial N-Boc-diethyl malonate. Although this method has been optimized previously with the N-Bz-hemimalonate analogue, this key step was reinvestigated with the N-Boc derivative to improve the required reaction time, the yield, and the diastereoselectivity. The new conditions enhance this transformation, and quantitative yields and anti/syn ratios up to 96:4 can be obtained. The anti aldol product was easily isolated in pure form and then taken forward as the key precursor in the preparation of both a set of ten N-/O-alkylated anti 2-amino-1,3-diol derivatives and the syn congeners.

Chiral Lithium Amido Zincates for Enantioselective 1,2-Additions: Auto-assembling Reagents Involving a Fully Recyclable Ligand.

A methodology consisting in carrying out enantioselective nucleophilic 1,2-additions (ee values up to 97 %) from cheap, easily accessible, and never described before, chiral lithium amido zincates is presented. These multicomponent reactants auto-assemble when mixing, in a 1:1 ratio, a homoleptic diorganozinc (R2 Zn) with a chiral lithium amide (CLA). The latter, obtained after a single reductive amination, plays the role of the chiral inductor and is fully recoverable thanks to a simple acid-base wash, allowing being recycled and re-use without loss of stereochemical information.

Synthesis and Identification of Aryl and Alkyl Gem-Dilithium Phosphido-Boranes: A Boost to the Chemistry of Phosphandiides.

The synthesis and identification of unprecedented gem-dianionic phosphorus compounds, that is, gem-dilithium phosphido-boranes Li2 [RP⋅BH3 ], with R=Ph or Cy, are reported in THF solution. These were obtained by double deprotonation of the corresponding primary phosphine-borane precursors RPH2 ⋅BH3 . Their in-depth structural study, based on multinuclear (1 H, 6 Li, 7 Li, 11 B, 13 C, 31 P) mono- and bi-dimensional NMR analyses, indicates a strong influence of the phosphorus substituent on the structure of the gem-dianionic phosphorus structure; a monomeric arrangement was obtained when R=phenyl, whereas a cyclic oligomer was observed for R=cyclohexyl. These compounds represent a new type of useful reagent, and their access paves the way for the concept of "RP synthons" (i.e., RP2- phosphandiides), likely to be the most flexible precursors of a variety of phosphorus targets.

A Combined 1 H/6 Li†NMR DOSY Strategy Finally Uncovers the Structure of Isopropyllithium in THF.

Despite its common use in synthesis, the structure of isopropylliyhium in THF has never been determined, a dimer being generally proposed but not supported. This paper fills this data gap through a sophisticated NMR study that shows that, in THF at low-temperature, isopropyllithium is in the form of a 1:2 mixture of a trisolvated monomer and a disolvated dimer in equilibrium. The presence of the monomer, never evoked before, together with a hypo-solvation of the dimer hinted by DFT calculations, provides a rational explanation to the remarkable reactivity of this organolithium reagent in ethereal solvents.

Chiral Lithium Amides: Tuning Asymmetric Synthesis on the Basis of Structural Parameters.

An overview on the structural arrangements adopted by Chiral Lithium Amides (CLAs), alone or in mixed complexes, is presented. These species are important reagents for asymmetric synthesis and understanding their organization is essential to improve their design and the reaction conditions.

Direct Carboxylation of Aryl Tosylates by CO2 Catalyzed by In situ-Generated Ni(0).

A novel Ni(0) -catalyzed carboxylation of aryl tosylates with carbon dioxide has been achieved under moderate temperatures and atmospheric pressure. In this procedure, the active Ni(0) species is generated in situ by simply mixing the Ni(0) precatalyst [NiBr2 (bipy)] with an excess of manganese metal. This approach requires neither a glove-box nor the tedious preparation of sophisticated intermediate organometallic derivatives. This mild, convenient, and user-friendly process is successfully applied to the valorization of carbon dioxide and the synthesis of versatile reactants with broad tolerance of substituents.

A Lithium Amide Protected Against Protonation in the Gas Phase: Unexpected Effect of LiCl.

In cold THF and in the presence of LiCl, a lithium pyrrolidinylamide forms a 1:1 mixed aggregate, which is observed directly by ESI-MS. Gas-phase protonation of this species leads to selective transfer of H(+) to the chlorine, suggesting that LiCl shields the amide nitrogen and prevents its direct protonation.

Probing solvent effects on mixed aggregates associating a chiral lithium amide and n-BuLi by NMR: from structure to reactivity.

An NMR study of a 1 : 1 mixture of a chiral lithium amide (4a) and n-BuLi shows that depending on the solvent employed (Et2O or THF) a mixed aggregate can form in proportions that are directly related to the ees measured during the enantioselective alkylation of o-tolualdehyde by these same species.

First substoichiometric version of the catalytic enantioselective addition of an alkyllithium to an aldehyde.

A substoichiometric enantioselective version of the extremely fast nucleophilic addition of Alk-Li to RCHO is made possible thanks to a thorough analysis of the aggregation phenomena involved in the reaction: calculated quantities of LiCl must be added to the medium at the right time to keep the catalytic cycle running.

Ph2P(BH3)Li: from ditopicity to dual reactivity.

A multinuclear NMR study shows that the deprotonation of diphenylphosphine-borane by n-BuLi in THF leads to a disolvated lithium phosphido-borane Ph(2)P(BH(3))Li of which Li(+) is connected to the hydrides on the boron and two THF molecules rather than to the phosphorus. This entity behaves as both a phosphination and a reducing agent, depending on the kinetic or thermodynamic control imposed to the reaction medium. Density functional theory computations show that H(2)P(BH(3))Li exhibits a ditopic character (the lithium cation can be in the vicinity of the hydride or of the phosphorus). It explains its dual reactivity (H- or P-addition), both routes going through somewhat similar six-membered transition states with low activation barriers.

MeLi + LiCl in THF: one heterodimer and no tetramers.

The structure of the aggregates formed when mixing methyllithium and lithium chloride in THF has been studied by multinuclear magnetic resonance at 170 K. The data suggest that only one new entity is observed, that is the dimer [(MeLi)(LiCl)], in equilibrium (K approximately 0.6) with [MeLi](4) and [LiCl](2). NMR diffusion measurements lead to the conclusion that this dimer is trisolvated in THF at 170 K, a solvation scheme in agreement with DFT computations.

Enantioselective conjugate addition of a lithium ester enolate catalyzed by chiral lithium amides: a possible intermediate characterized.

Two 1:1 noncovalent mixed aggregates between a lithium enolate and two diastereomeric lithium amides have been identified spectroscopically in THF. The NMR data, as well as DFT theoretical calculations, shine some light on a puzzling reversal of induction, observed when switching from one diastereomer of the amide to the other in the enantioselective Michael addition of the lithium enolate to an unsaturated ester.

Shuffling lithiated mixed aggregates: NMR and Car-Parrinello molecular dynamics reveal an unexpected associative pathway.

The exchange of Me(6)Li aggregated to a lithium amide by (7)LiCl leads to a specific isotope distribution whose microscopic origin is assigned to an edge-to-edge interaction between the R(2)NLi-MeLi aggregate and (LiCl)(2) by NMR and Car-Parrinello molecular dynamics.

Heterocyclic lithium amides as chiral ligands for an enantioselective hydroxyalkylation with n-BuLi.

Chiral heterocyclic structures based on 3-aminopyrrolidines (3APs), 3-aminotetrahydrothiophens (3ATTs), and 3-aminotetrahydrofurans (3ATFs) have been synthesized. The corresponding lithium amides have been evaluated as chiral ligands in the condensation of n-BuLi on o-tolualdehyde. The returned levels of induction were in the 46-80% ee range. The cheap and easily prepared 3ATFLi's turned out to be also the best ligands, giving access to the expected R or S alcohols in a same 80% level of induction at -78 degrees C in THF. In all cases, the sense of induction depends on the absolute configuration of C(8) on the 3-amino appendage. A general concept is proposed to rationalize the process of induction in the presence of organolithium species.