Albert Guijarro

On the Mechanism of Arene‐Catalyzed Lithiation: The Role of Arene Dianions—Naphthalene Radical Anion versus Naphthalene Dianion

The use of lithium and a catalytic amount of an arene is a well-established methodology for the preparation of organolithium reagents that manifest greater reactivity than the classical lithium-arene solutions. In order to rationalize this conduct, the participation of a highly reduced species, the dianion, is proposed and its reactivity explored. Studies of kinetics and of distribution of products reveal that the electron-transfer (ET) reactivity profile of dilithium naphthalenide in its reaction with organic chlorides excludes alternative mechanisms of halogen-lithium exchange. The process generates organolithium compounds. The dianion thus emerges along with the radical anion as a suitable candidate for catalytic cycles in certain processes. Endowed with a higher redox potential than its radical anion counterpart, dilithium naphthalene displays a broader spectrum of reactivity and so increases the range of substrates suitable for lithiation. The reaction of dilithium naphthalene with THF is one example of the divergent reactivity of the radical anion and the dianion, which has been the source of apparent misinterpretation of results in the past and has now been appropriately addressed.

On the mechanism of the naphthalene-catalysed lithiation: the role of the naphthalene dianion

Abstract Kinetic and distribution product studies on naphthalene-catalysed lithiation reactions of chlorinated precursors have shown the probable participation of a naphthalene dianion (dilithium naphthalene) as the very active electron carrier agent in the chlorine–lithium exchange process.

Naphthalene-catalysed lithiation of functionalized chloroarenes : regioselective preparation and reactivity of functionalized lithioarenes

Abstract The lithiation of different functionalized chloroarenes (dichlorobenzenes 1 and 3, mono and dichlorophenols 9 and 14, and chloropivalanilides 18) in the presence of a catalytic amount of naphthalene leads to the corresponding functionalized lithioarenes, which react with electrophiles to give the expected polyfunctionalized aromatic molecules 2, 4, 10, 19, 21, 22 and 24 in a regioselective manner. In the case of starting from chlorinated phenols or anilides a deprotonation of the functional group is carried out prior to the lithiation process; only for 2-chloropivalanilide 18o a coupling reaction leading to 2-n-butylpivalanilide is observed when an excess of n-butyllithium is used in the deprotonation step.

4,4′-Di-tert-butylbiphenyl-catalysed lithiation of chloromethyl ethyl ether: A barbier-type new and easy alternative to ethyl lithiomethyl ether

The reaction of an equimolar amount of chloromethyl ethyl ether (1) and different carbonyl compounds (2) with an excess of lithium powder (1:7 molar ratio) in the presence of a catalytic amount of 4,4′-di-tert-butylbiphenyl (5 mol %) in THF at 0°C leads, after hydrolysis, to the corresponding hydroxyethers 3.

4,4′-di-tert-butylbiphenyl-catalysed lithiation of 2,3-dichloropropene: A Barbier-type practical alternative to 2,3-dilithiopropene

Abstract The reaction of 2,3-dichloropropane ( 1 ) and different carbonyl compounds ( 2 ) with an excess of lithium powder (1:7 molar ratio) in the presence

On the dichotomy of the SN2/ET reaction pathways: an apparent SN2 reactivity in the reaction of naphthalene dianion with alkyl fluorides

Abstract Dilithium naphthalene (Li2C10H8) displays a SN2 reactivity profile in its reaction with alkyl fluorides (n-, s- and t-octyl fluoride). SN2 seems to be the dominant mechanism operating with primary alkyl fluorides, which presumably turns into competition with ET as we move to secondary and tertiary alkyl fluorides. Significantly, lithium naphthalene (LiC10H8) seems to have also an important nucleophilic component when reacting with alkyl fluorides, in contrast to the previously proposed general ET process valid for all alkyl halides. These results explain the observed distribution of products and are reinforced by a complete analysis of the products originated by the reaction with 6-halohexenyl radical probes, whose main alkylation products are described here for the first time.

Primary alkyl fluorides as regioselective alkylating reagents of lithium arene dianions. Easy prediction of regioselectivity by MO calculations on the dianion

Lithium arene dianions derived of polycyclic aromatic hydrocarbons, such as naphthalene, anthracene, phenanthrene, fluoranthene, pyrene, chrysene and binaphtyl react cleanly with n-alkylfluorides to afford regiochemically controlled alkylated dihydroarenes after hydrolysis. These arene dianions can be easily prepared by simple treatment of the arene with lithium in THP. Unlike simple radical coupling, the alkylation of these species with alkyl fluorides apparently goes through a SN2 transition state, despite the inertness of alkyl fluorides to undergo nucleophilic substitution. It is also atypical for reduced arenes, which tend to give ET reactions with other alkyl halides. Prediction of the regiochemistry was easily conducted by means of MO calculations (PM3) on the dianion, and in all cases were consistent with the experimental.

Polychlorinated materials as a source of polyanionic synthons

Abstract The reaction of dichloromethane ( 1a ) or dichlorodideuteriomethane ( 1b ) with an excess of lithium powder (1:7 molar ratio) and a catalytic amount of DTBB (5 mol %) in the presence of a carbonyl compound 2 (1:2 molar ratio) in THF at −40°C yields, after hydrolysis, the corresponding 1,3-diols 3 in moderate yields. The process is applied to other gem -dichlorinated materials such as 7,7-dichloro[4.1.0]heptane ( 4 ), 1,1-dichlorotetramethylcyclopropane ( 7 ) and dichloromethyl methyl ether ( 10 ), using pivalaldehyde as electrophile. Starting from 1,1,1-trichlorinated compounds or tetrachloromethane ( 14 ) and using chlorotrimethylsilane as electrophile at temperatures ranging between −80 and −90°C, the corresponding polysilylated compounds 15–17 are prepared applying the mentioned methodology.

DTBB-catalysed lithiation of 2,3-dichloropropene and related chloroamines: Synthetic applications

Abstract The reaction of 2,3-dichloropropene ( 1 ) and different carbonyl compounds ( 2 ) with an excess of lithium powder (1:7 molar ratio) in the presence of a catalytic amount of DTBB (5 mol %) in THF at 0°C leads, after hydrolysis with water, to the corresponding methylenic 1,4-diols 3 in a Barbier-type process. The cyclisation of diols 3 under acidic conditions (hydrochloric or phosphoric acid) yields the corresponding substituted methylenic tetrahydrofurans 4 . Finally, 2,3-dichloropropene ( 1 ) is converted into the corresponding allylic chloroamines 5 and then submitted to the tandem naphthalene-catalysed 2lithiation-S E reaction with different electrophiles affording the corresponding functionalised amines 7 . The last process fails for oxygen- or sulfur-containing chloroallylic materials 8 .

Crystal structure and electronic states of tripotassium picene

The crystal structure of potassium doped picene with an exact stoichiometry (K3picene) has been theoretically determined within Density Functional Theory allowing complete variational freedom of the crystal structure parameters and the molecular atomic positions. A modified herringbone lattice is obtained in which potassium atoms are intercalated between two paired picene molecules displaying the two possible orientations in the crystal. Along the c-axis, organic molecules alternate with chains formed by three potassium atoms. The electronic structure of the doped material resembles pristine picene, except that now the bottom of the conduction band is occupied by six electrons coming from the ionized K atoms (six per unit cell). Wavefunctions remain based mainly on picene molecular orbitals getting their dispersion from intralayer edge to face CH/ bonding, while eigenenergies have been modified by the change in the electrostatic potential. The small dispersion along the c axis is assigned to small H-H overlap. From the calculated electronic density of states we expect metallic behavior for potassium doped picene.