Cristian Vidal

Introducing Deep Eutectic Solvents to Polar Organometallic Chemistry: Chemoselective Addition of Organolithium and Grignard Reagents to Ketones in Air

Despite their enormous synthetic relevance, the use of polar organolithium and Grignard reagents is greatly limited by their requirements of low temperatures in order to control their reactivity as well as the need of dry organic solvents and inert atmosphere protocols to avoid their fast decomposition. Breaking new ground on the applications of these commodity organometallics in synthesis under more environmentally friendly conditions, this work introduces deep eutetic solvents (DESs) as a green alternative media to carry out chemoselective additions of ketones in air at room temperature. Comparing their reactivities in DES with those observed in pure water suggest that a kinetic activation of the alkylating reagents is taking place, favoring nucleophilic addition over the competitive hydrolysis, which can be rationalized through formation of halide-rich magnesiate or lithiate species.

Deep eutectic solvents: biorenewable reaction media for Au(I)-catalysed cycloisomerisations and one-pot tandem cycloisomerisation/Diels–Alder reactions

Cycloisomerisation reactions of (Z)-enynols into furans can be conveniently performed, for the first time, in the eutectic mixture 1ChCl/2Gly as a solvent and under standard bench conditions (at room temperature and under air) by using the new bis(iminophosphorane)–Au(I) complex [Au2Cl2(μ2-S,S-CH2{P(NP(S)(OPh)2)Ph2}2)] as a catalyst. Furthermore, a one-pot tandem reaction involving the fast cycloisomerisation of (Z)-enynols followed by an intermolecular atom economical process, i.e. the Diels–Alder reaction with activated alkynes or alkenes, is reported. This tandem cycloisomerisation/Diels–Alder reaction proceeds also in the eutectic mixture 1ChCl/2Gly, in the absence of co-catalysts and under aerobic conditions, giving rise to the corresponding 7-oxanorbornadienes and 7-oxanorbornenes under the principles of the so-called Green Chemistry.

Exploiting Deep Eutectic Solvents and Organolithium Reagent Partnerships: Chemoselective Ultrafast Addition to Imines and Quinolines Under Aerobic Ambient Temperature Conditions

Shattering the long-held dogma that organolithium chemistry needs to be performed under inert atmospheres in toxic organic solvents, chemoselective addition of organolithium reagents to non-activated imines and quinolines has been accomplished in green, biorenewable deep eutectic solvents (DESs) at room temperature and in the presence of air, establishing a novel and sustainable access to amines. Improving on existing methods, this approach proceeds in the absence of additives; occurs without competitive enolization, reduction or coupling processes; and reactions were completed in seconds. Comparing RLi reactivities in DESs with those observed in pure glycerol or THF suggests a kinetic anionic activation of the alkylating reagents occurs, favoring nucleophilic addition over competitive hydrolysis.

Pd(II)-catalyzed cycloisomerisation of γ-alkynoic acids and one-pot tandem cycloisomerisation/CuAAC reactions in water

Cycloisomerisation reactions of γ-alkynoic acids into cyclic enol-lactones can be conveniently performed in pure water as a solvent and under aerobic conditions by using a novel iminophosphorane–Pd(II) complex trans-[PdCl2{μ2-N,S-(PTA)NP(S)(OEt)2}]2 as a catalyst. It is important to note that the catalytic system could be recycled up to 10 consecutive runs. In addition and for the first time, a one-pot tandem orthogonal reaction involving the fast cycloisomerisation of γ-alkynoic acids, followed by an intermolecular atom economical process, i.e. the 1,3-dipolar cycloaddition of azides with terminal alkynes (CuAAC), is reported. This new tandem cycloisomerisation/click reaction proceeds also in water, at room temperature and under aerobic conditions, giving rise to unprecedented bicyclic triazol-enol-lactones under the principles of the so called “Green Chemistry”.

From a Sequential to a Concurrent Reaction in Aqueous Medium: Ruthenium‐Catalyzed Allylic Alcohol Isomerization and Asymmetric Bioreduction

The ruthenium-catalyzed redox isomerization of allylic alcohols was successfully coupled with the enantioselective enzymatic ketone reduction (mediated by KREDs) in a concurrent process in aqueous medium. The overall transformation, formally the asymmetric reduction of allylic alcohols, took place with excellent conversions and enantioselectivities, under mild reaction conditions, employing commercially and readily available catalytic systems, and without external coenzymes or cofactors. Optimization resulted in a multistep approach and a genuine cascade reaction where the metal catalyst and biocatalyst coexist from the beginning.

New Ag(I)–Iminophosphorane Coordination Polymers as Efficient Catalysts Precursors for the MW-Assisted Meyer–Schuster Rearrangement of Propargylic Alcohols in Water

Treatment of the N-thiophosphorylated iminophosphorane ligands (PTA)═NP(═S)(OR)2 [PTA = 1,3,5-triaza-7-phosphaadamantane, 3a and 3b] and (DAPTA)═NP(═S)(OR)2 [DAPTA = 3,7-diacetyl-1,3,7-triaza-5-bicyclo[3.3.1]nonane, 4a and 4b] with an equimolecular amount of AgSbF6 leads to high-yield formation of the new one-dimensional coordination polymers [Ag{μ(2)-N,S-(PTA)═NP(═S)(OR)2}]x[SbF6]x (5a and 5b) and [Ag{μ(2)-O,S-(DAPTA)═NP(═S)(OR)2}]x[SbF6]x (6a and 6b), respectively. These new (iminophosphorane)silver(I) coordination polymers are efficient catalyst precursors for the Meyer-Schuster isomerization of both terminal and internal alkynols. Reactions proceeded in water, under aerobic conditions and using microwave irradiation as heating source, to afford the corresponding α,β-unsaturated carbonyl compounds in excellent yields, without the addition of any cocatalyst. Remarkably, it should be noted that this catalytic system can be recycled up to 10 consecutive runs (1st cycle 45 min, 99%; 10th cycle 6 h, 97%). ESI-MS analysis of 5a in water has been carried out providing valuable insight into the monomeric active species responsible for catalytic activity in water.

Synthesis and reactivity of new rhenium(I) complexes containing iminophosphorane-phosphine ligands: application to the catalytic isomerization of propargylic alcohols in ionic liquids.

[ReBr(CO)5] reacts with the iminophosphorane-phosphine ligands Ph2PCH2P(═NR)Ph2 (R = P(═O)(OEt)2 (1a), P(═O)(OPh)2 (1b), P(═S)(OEt)2 (1c), P(═S)(OPh)2 (1d), 4-C6F4CHO (1e), 4-C6F4CN (1f), 4-C5F4N (1g)) affording the neutral complexes [ReBr(κ(2)-P,X-Ph2PCH2P{═NP(═X)(OR)2}Ph2)(CO)3] (X = O, R = Et (2a), Ph (2b); X = S, R = Et (2c), Ph (2d)) and [ReBr{κ(2)-P,N-Ph2PCH2P(═NR)Ph2}(CO)3] (R = P(═O)(OEt)2 (3a), P(═O)(OPh)2 (3b), 4-C6F4CHO (3e), 4-C6F4CN (3f), 4-C5F4N (3g)). The reactivity of the cationic complex [Re(κ(3)-P,N,S-Ph2PCH2P{═NP(═S)(OPh)2}Ph2)(CO)3][SbF6] (4d) has been explored allowing the synthesis of the cationic [Re(L)(κ(2)-P,S-Ph2PCH2P{═NP(═S)(OPh)2}Ph2)(CO)3][SbF6] (L = acetone (5a), CH3C≡N (5b), pyridine (5c), PPh3 (5d)) and the neutral [ReY(κ(2)-P,S-Ph2PCH2P{═NP(═S)(OPh)2}Ph2)(CO)3] (Y = Cl (6a), I (6b), N3 (6c)) complexes. The catalytic activity of complex 4d in the regioselective isomerization of terminal propargylic alcohols HC≡CCR(1)R(2)(OH) into α,β-unsaturated aldehydes R(1)R(2)C═CHCHO or ketones R(3)R(4)C═CR(1)COMe (if R(2) = CHR(3)R(4)) under neutral conditions in ionic liquids has being studied. Isolation and X-ray characterization of the key intermediate rhenium(I) oxocyclocarbene complex [Re{═C(CH2)3O}(κ(2)-P,S-Ph2PCH2P{═NP(═S)(OPh)2}Ph2)(CO)3][SbF6] (5e) seems to indicate that the catalytic reaction proceeds through tautomerization of the terminal alkynols to yield vinilydene-type species.