Cecilia Gómez

POLYMER SUPPORTED ARENE-CATALYSED LITHIATION REACTIONS

Abstract The reaction of functionalised mono or dichlorinated materials 1a–6a with an excess of lithium and a catalytic amount of a naphthalene (P N ) or biphenyl (P B ) supported polymer (eassily prepared by radical copolymerisation of 2-vinylnaphthalene or 4-vinylbiphenyl with vinylbenzene and divinylbenzene) in THF either in the presence or not of different electrophiles [Me 3 SiCl, i PrCHO, PhCHO, Et 2 CO, (CH 2 ) 4 CO, (CH 2 ) 5 CO, ( c -C 3 H 5 ) 2 CO, i Pr 2 CO, PhCOMe, PhCHNPh] at −78 or −50°C leads, after hydrolysis with water, to the expected functionalised products 1ca–6ck . The polymeric catalyst is quantitatively recovered and can reused several times without any loss of activity.

Polymer supported naphthalene-catalysed lithiation reactions

Abstract The reaction of functionalised mono or dichlorinated materials 1a–6a with an excess of lithium and a catalytic amount of a naphthalene supported polymer (P-152, easily prepared by radical copolymerisation of 2-vinylnaphthalene, styrene and divinylbenzene) in THF either in the presence (Barbier-type conditions) or not of different electrophiles [Me 3 SiCl, Bu n CHO, Bu i CHO, PhCHO, Et 2 CO, c (C 3 H 5 ) 2 CO, Pr i 2 CO, (CH 2 ) 4 CO, (CH 2 ) 5 CO, PhCOMe, PhCHNPh] leads, after hydrolysis, to the expected products 1c–6c . The catalyst is quantitatively recovered and can be reused several times without any loss of its activity.

Naphthalene-catalysed lithiation of 3-chloro-2-chloromethylpropene in a Barbier-type process with carbonyl compounds☆

Abstract The reaction of 3-chloro-2-chloromethylpropene ( 1 ) and carbonyl compounds ( 2 ) with an excess of lithium powder in the presence of a catalytic amount of naphthalene (6%) in tetrahydrofuran at −78 to 20°C leads, after hydrolysis, to the corresponding methylenic 1,5-diols 3 in a Barbier-type process. The treatment of the crude diols 3 with 12 M. hydrochloric acid affords selectively the corresponding substituted dihydropyrans 6 .

Polyphenylene as an electron transfer catalyst in lithiation processes

Abstract The lithiation of different functionalised chlorinated materials ( 1a – c ), dichlorinated compounds ( 1d – f ) and benzofused cyclic ethers ( 1g , h ) with lithium powder in the presence of catalytic amounts of either linear (LPP) or crosslinked (CPP) polyphenylene, in THF at temperatures ranging between −78 and 20°C, leads to the expected organolithium intermediates ( Ia – h ), which by reaction with electrophiles [Bu t CHO, PhCHO, Et 2 CO, (CH 2 ) 5 CO, PhCOMe, Me 3 SiCl] gives, after hydrolysis with water, the expected products 2aa – hf .

DTBB-catalysed lithiation of chlorinated benzylic chlorides, alcohols, thiols or amines

The reaction of chlorinated benzyl chlorides (1) with an excess of lithium powder and a catalytic amount of DTBB (4 mol %) in the presence of different electrophiles [PriCHO, ButCHO, Et2CO, (CH2)5CO, PhCOMe, Me3SiCl] in THF at −50°C followed by hydrolysis with water leads to the corresponding compounds 2. When the same DTBB-catalysed lithiation is applied to several chlorinated benzylic alcohols or mercaptans (4 or 5) it is necessary to deprotonate the starting material with BunLi; treatment of the resulting anions or amine 6 as above, but at −78°C, leads to the expected reaction products 8, after reaction with different electrophiles [PriCHO, ButCHO, Et2CO, (CH2)5CO, PhCOMe, Me3SiCl] and final hydrolysis with water.

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 .

Lithiation Reactions Catalyzed by Linear and Cross-Linked Arene-Based Polymers. Generation of Functionalized Organolithium Compounds

Lithiation of various substrates, such as chlorinated acetals, α-chloro ether, dichloro derivatives benzo-fused heterocycles, and allyl and benzyl derivatives, with excess lithium powder in the presence of a catalytic amount of soluble linear or insoluble cross-linked arene (naphthalene or biphenyl)-based polymers yields the expected organolithium intermediates. The latter react with electrophiles either in two steps or under Barbier-type reaction conditions to afford the corresponding adducts. The catalyst is easily recuperated by filtration at the end of the process, and the procedure can be regarded as a reasonable alternative to the use of free arenes as electron carrier in lithiation reactions.

Lithiated benzyllithiums from chlorobenzyl chlorides by a DTBB-catalysed lithiation

Abstract The reaction of 2-, 3- or 4-chlorobenzyl chlorides ( 1a-c ) with an excess of lithium and a catalytic amount of DTBB (7 mol%) in the presence of different electrophiles [Pr i CHO, Bu t CHO, Et 2 CO, (CH 2 ) 5 CO, PhCOMe, Me 3 SiCl] in THF at −50°C leads after hydrolysis with water, to the expected dioles or disilylated compounds 2aa-2cf .

The first direct formation of an organolithium reagent on a soluble polymer by chlorine–lithium exchange: functionalised linear polystyrene

Abstract The lithiation of a soluble chloromethylated polystyrene 1 (prepared by AIBN-induced copolymerisation of styrene and 4-chloromethylstyrene in 3:1 molar ratio) with an excess of lithium powder and a catalytic amount (10%) of DTBB, and reaction with different electrophiles leads, after hydrolysis, to the expected functionalised polymers 2–8 .

Recent Advances in Asymmetric Organocatalyzed Conjugate Additions to Nitroalkenes

The asymmetric conjugate addition of carbon and heteroatom nucleophiles to nitroalkenes is a very interesting tool for the construction of highly functionalized synthetic building blocks. Thanks to the rapid development of asymmetric organocatalysis, significant progress has been made during the last years in achieving efficiently this process, concerning chiral organocatalysts, substrates and reaction conditions. This review surveys the advances in asymmetric organocatalytic conjugate addition reactions to α,β-unsaturated nitroalkenes developed between 2013 and early 2017.