The Allylic Alkylation of Ketone Enolates

The palladium-catalyzed allylic alkylation of non-stabilized ketone enolates was thought for a long time to be not as efficient as the analogous reactions of stabilized enolates, e. g. of malonates and β-ketoesters. The field has experienced a rapid development during the last two decades, with a range of new, highly efficient protocols evolved. In this review, the early developments as well as current methods and applications of palladium-catalyzed ketone enolate allylations will be discussed.     

Stereoselective Synthesis of Trisubstituted Vinylboronates from Ketone Enolates Triggered by 1,3‐Metalate Rearrangement of Lithium Enolates

An unprecedented stereoselective synthesis of trisubstituted vinylboronates is reported to proceed by direct borylation of lithium ketone enolates under transition‐metal‐free conditions. The stereospecific C?O borylation of lithium enolates was triggered by a carbonyl‐induced 1,3‐metalate rearrangement via a C‐bound boron enolate. DFT calculations and control experiments revealed that the stereoselectivity is controlled by sterics. A variety of stereospecific trisubstituted vinylboronates, together with several tetrasubstituted vinylboronates, were conveniently synthesized with the newly developed methodology. Based on the transformation of stereospecific vinylboronate, a single isomer of Dienestrol was efficiently obtained.     

Tetrameric Cubic Structures of Two Solvated Lithium Enolates

The structures of the crystalline lithium enolates derived from 3, 3-dimethyl-2-butanone and from cyclopentanone have been determined by X-ray analysis. Both structures are tetrameric aggregates based on a Li₄O₄-cube, each Li⁺-ion being additionally bonded to the O-atom of a tetrahydrofuran solvent molecule.     

Palladium‐Catalyzed Asymmetric Allylic Alkylation of Ketone Enolates

Palladium‐catalyzed asymmetric allylic alkylation of nonstabilized ketone enolates to generate quaternary centers has been achieved in excellent yield and enantioselectivity. Optimized conditions consist of performing the reaction in the presence of two equivalents of LDA as base, one equivalent of trimethytin chloride as a Lewis acid, 1,2‐dimethoxyethane as the solvent, and a catalytic amount of a chiral palladium complex formed from π‐allyl palladium chloride dimer 3 and cyclohexyldiamine derived chiral ligand 4 . Linearly substituted, acyclic 1,3‐dialkyl substituted, and unsubstituted allylic carbonates function well as electrophiles. A variety of α‐tetralones, cyclohexanones, and cyclopentanones can be employed as nucleophiles. The absolute configuration generated is consistent with the current model in which steric factors control stereofacial differentiation. The quaternary substituted products available by this method are versatile substrates for further elaboration.     

Reactions of Zinc Enolates Derived from 1-Aryl-2,2-dibromoalkanones with 3-Acetyl-6-bromochromen-2-one

Zinc enolates derived from substituted 1-aryl-2,2-dibromoalkanones react with 3-acetyl-6-bromochromen-2-one to give 1a-acetyl-1-alkyl-1-aroyl-6-bromo-1a,7b-dihydro-1H-cyclopropa[c]chromen-2-ones as a single stereoisomer.     

Cyclopropanation of N-Substituted 2-Oxochromene- and 6-Bromo-2-oxochromene-3-carboxamides with Zinc Enolates Derived from 1-Aryl-2,2-dibromoalkanones

Zinc enolates derived from 1-aryl-2,2-dibromoalkanones react with N-cyclohexyl-2-oxochromene-3-carboxamides to give N-cyclohexyl-1-alkyl-1-aroyl-2-oxo-1a,7b-dihydrocyclopropa[c]chromene-1a-carboxamides mainly as cis isomers with respect to the substituents in positions 1 and 1a. Reactions of the same zinc enolates with N-benzyl-2-oxochromene-3-carboxamide and N-benzyl-6-bromo-2-oxochromene-3-carboxamide lead to formation of 1-aryl-2-benzyl- and 1-aryl-2-benzyl-6-bromo-1-hydroxy-9c-alkyl-1,2,9b,9c-tetrahydro-5-oxa-2-azacyclopenta[2,3]cyclopropa[1,2-a]naphthalene-3,4-diones. The reaction of zinc enolates with N-aryl-2-oxochromene-3-carboxamides in a weakly polar solvent (diethyl ether or ethyl acetate) affords mixtures of cis-N-aryl-1-aroyl-1-alkyl-2-oxo-1a,7b-dihydrocyclopropa[c]chromene-1a-carboxamides and their cyclic isomers, 9c-alkyl-1,2-diaryl-1-hydroxy-1,2,9b,9c-tetrahydro-5-oxa-2-azacyclopenta[2,3]cyclopropa[1,2-a]naphthalene-3,4-diones, the latter prevailing. N-Substituted 1-alkyl-1-aroyl-2-oxo-1a,7b-dihydrocyclopropa[c]chromene-1a-carboxamides in which the aroyl group on C¹ and the carboxamide group on C^1a are arranged trans are formed by reactions of zinc enolates with the corresponding 2-oxochromene-3-carboxamides in the presence of hexamethylphosphoric triamide.__________Translated from Zhurnal Organicheskoi Khimii, Vol. 41, No. 4, 2005, pp. 539–546.Original Russian Text Copyright © 2005 by V. Shchepin, Silaichev, R. Shchepin, Ezhikova, Kodess.     

Mechanistic Implications of the Tetrameric Cubic Structure of Lithium Enolates

The tetrameric cubic structure established for lithium enolates in the solid state is used as a model to discuss several facets of enolate chemistry: solubility, effects of cosolvents, addition to aldehyde and acid chloride, influence of mixed aggregates on diastereo- and enantioselectivities.     

Lithium norcaranylidenoids. Alkylation and epimerization

The epimeric 7-bromo-7-lithionorcaranes have been stereospecifically generated; the $\text{exo}$-bromo isomer is stable at ?78°C, while the $\text{endo}$- bromo isomer is reactive. The stereochemistry of its reaction with nBuLi involves inversion.     

Reaction of Zinc Enolates Derived from Substituted 2,2-Dibromobutyrophenones with Ethyl 5,5-Dimethyl-2-oxo-2,5-dihydrofuran-3-carboxylate

Zinc enolates derived from substituted 2,2-dibromobutyrophenones react with ethyl 5,5-dimethyl-2-oxo-2,5-dihydrofuran-3-carboxylate to give ethyl 6-aroyl-6-ethyl-4,4-dimethyl-2-oxo-3-oxabicyclo[3.1.0]-hexane-1-carboxylates mostly as a single geometric isomer.     

Regioselective Synthesis of Functionalized Dihydroquinolines via Organocatalytic Allylic Alkylation

The regioselective allylic alkylation of 1,2-dihydroquinolines and Morita-Baylis-Hillman(MBH) adducts has been developed. By surveying various reaction parameters, we summarized the effects of temperatures, relative reactant doses, catalysts, solvents and N-protected groups on the regioselectivity of this transformation. This method provides a facile protocol for the preparation of allylic α-substituted dihydroquinolines.     

Alkylation with Substituted Phenacyl Bromides of Sodium Enolates from 6-Aryl-3,5,5-trimethyl-2,3,5,6-tetrahydropyran-2,4-diones

Russian Journal of Organic Chemistry -     

Aggregation and Cooperative Effects in the Aldol Reactions of Lithium Enolates

Density functional theory and Car–Parrinello molecular dynamics simulations have been carried out for model aldol reactions involving aggregates of lithium enolates derived from acetaldehyde and acetone. Formaldehyde and acetone have been used as electrophiles. It is found that the geometries of the enolate aggregates are in general determined by the most favorable arrangements of the point charges within the respective Li_nO_n clusters. The reactivity of the enolates follows the sequence monomer?dimer>tetramer. In lithium aggregates, the initially formed aldol adducts must rearrange to form more stable structures in which the enolate and alkoxide oxygen atoms are within the respective Li_nO_n clusters. Positive cooperative effects, similar to allosteric effects found in several proteins, are found for the successive aldol reactions in aggregates. The corresponding transition structures show in general sofa geometries.     

Polybromoaromatic Compounds: IX. Reactions of Polybromobenzyl Bromides with Enolates Derived from Some Dicarbonyl Compounds

The reaction of polybromobenzyl bromides RC₆Br₄CH₂Br (R = Br, OCH₃) with diethyl malonate sodium salt in ethanol and dimethylformamide leads to formation of diethyl 2-(polybromobenzyl)malonates, whereas in aqueous ethanol ethyl polybromobenzyl malonates are formed. The same polybromobenzyl bromides react with an equimolar amount of ethyl acetoacetate sodium salt or acetylacetone sodium salt to give C-alkylation products; with excess sodium enolates ethyl 3-(polybromophenyl)propionates and 4-(polybromophenyl)-2-butanones are formed, respectively.     

Advanced Lithium Extraction Membranes Derived from Tagged-Modification of Polyamide Networks

Efficient Mg²⁺/Li⁺ separation is crucial to combating the lithium shortage worldwide, yet current nanofiltration membranes suffer from low efficacy and/or poor scalability, because desirable properties of membranes are entangled and there is a trade-off. This work reports a “tagged-modification” approach to tackle the challenge. A mixture of 3-bromo-trimethylpropan-1-aminium bromide (E₁) and 3-aminopropyltrimethylazanium (E₂) was designed to modify polyethylenimine – trimesoyl chloride (PEI-TMC) membranes. E₁ and E₂ reacted with the PEI and TMC, respectively, and thus, the membrane properties (hydrophilicity, pore sizes, charge) were untangled and intensified simultaneously. The permeance (34.3 L m⁻² h⁻¹ bar⁻¹) and Mg²⁺/Li⁺ selectivity (23.2) of the modified membranes are about 4 times and 2 times higher than the pristine membrane, and they remain stable in a 30-days test. The permeance is the highest among all analogous nanofiltration membranes. The tagged-modification method enables the preparation of large-area membranes and modules that produce high-purity lithium carbonate (Li₂CO₃) from simulated brine.     

Carbonylation of Lithium Enolates of Esters and Amides with Carbon Monoxide and Selenium

Abstract

Lithium enolates of esters, amides, and an acylsilane undergo carbonylation with carbon monoxide with the aid of selenium under mild conditions to yield the corresponding selenol esters after trapping with alkyl iodides.     

Regioselective Alkylation of 5-Substituted Tetrazoles with 3-Chlorobut-2-en-1-ol in Acid Medium

Russian Journal of Organic Chemistry - The alkylation of 5-R-tetrazoles (R = H, Me, Ph) with 3-chlorobut-2-en-1-ol was studied in 1,2-dichloroethane, chlorofom, and methylene chloride in the...     

Regioselective Alkylation Of Polycyclic Thiophene Derivatives By Butyllithium And Alkyl Halide

Polycyclic thiophene derivatives including the bisthiophene have been regioselectively alkylated by n-BuLi, and methyl iodide/ and allyl bromide.