Michael addition of Grignard reagents to tetraethyl ethenylidenebisphosphonate

Tetraethyl ethenylidenebisphosphonate can undergo facile Michael type addition reaction with simple Grignard reagents to give alkyl, arylalkyl, aryl C-substituted methylene bisphosphonates. This addition easily occurs even if funtionalised Grignard reagents are used.     

Asymmetric Conjugate Addition of Grignard Reagents to 3‐Silyl Unsaturated Esters for the Facile Preparation of Enantioenriched β‐Silylcarbonyl Compounds and Allylic Silanes

A highly enantioselective conjugate addition of Grignard reagents to 3‐silyl unsaturated esters to deliver synthetically useful chiral β‐silylcarbonyl compounds was developed. The synthetic value of this methodology was further illustrated by the synthesis of enantioenriched β‐hydroxyl esters and the facile access granted to various α‐chiral allylic silanes. A plethora of diastereoselective transformations of β‐silylenolates were also investigated and afforded manifold organosilanes that contained contiguous stereogenic centers with excellent enantioselectivity.     

Copper-Catalyzed Addition of Grignard Reagents to in situ Generated Indole-Derived Vinylogous Imines

Chiral indole derivatives are ubiquitous motifs in pharmaceuticals and alkaloids. Herein, the first protocol for catalytic asymmetric conjugate addition of Grignard reagents to various sulfonyl indoles, offering a straightforward approach for the synthesis of chiral 3-sec-alkyl-substituted indoles in high yields and enantiomeric ratios is presented. This methodology makes use of a chiral catalyst based on copper phosphoramidite complexes and in situ formation of vinylogous imine intermediates.     

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.     

Catalytic Reactions of Titanium Alkoxides with Grignard Reagents and Imines: A Mechanistic Study

The reactivity of Grignard reagents towards imines in the presence of catalytic and stoichiometric amounts of titanium alkoxides is reported. Alkylation, reduction, and coupling of imines take place. Whereas reductive coupling is the major reaction in stoichiometric reactions, alkylation is favored in catalytic reactions. Mechanistic studies clearly indicate that intermediates involved in the two reactions are different. Catalytic reactions involve a metal–alkyl complex. This has been confirmed by reactions of deuterium‐labeled substrates and different alkylating agents. Under the stoichiometric conditions, however, titanium olefin complexes are formed through reductive elimination, probably through a multinuclear intermediate.     

Copper-catalyzed enantioselective conjugate addition of Grignard reagents to acyclic enones using monodentate phosphoramidite ligands

Herein, we report efficient catalysts based on phosphoramidites for the asymmetric copper-catalyzed conjugate addition of Grignard reagents to acyclic α,β-unsaturated ketones. A variety of Grignard reagents can be added to aliphatic and aromatic acyclic enones with good yields and moderate to good enantioselectivities.     

Alkylation of Pyridines at Their 4‐Positions with Styrenes plus Yttrium Reagent or Benzyl Grignard Reagents

A new regioselective alkylation of pyridines at their 4‐position was achieved with styrenes in the presence of yttrium trichloride, BuLi, and diisobutylaluminium hydride (DIBAL‐H) in THF. Alternatively, similar products were more simply prepared from pyridines and benzyl Grignard reagents. These reactions are not only a useful preparation of 4‐substituted pyridines but are also complementary to other relevant reactions usually giving 2‐substituted pyridines.     

Identification of a four-center intermediate in a Grignard addition reaction to a P-S bond

The reaction between tert-butylmagnesium chloride (or tert-pentylmagnesium chloride) and the particular phosphorus-sulfur bond of a benzothiadiphospholic system showed, for the first time, evidence of formation of intermediates with a four-center structure. The possibility, for the phosphorus atom, to have very stable hypervalent coordinations makes it possible to observe its hypervalent states during the course of a reaction. The benzothiadiphosphole, with its bicyclic folded structure, further stabilizes the hypervalent coordinations thus making the intermediates sufficiently stable to be detected during the course of the reaction by ³¹P NMR spectroscopy, which revealed the nature and the stability of the species involved in this reaction, carried out also using other Grignard reagents.     

Cu‐Catalyzed Asymmetric Allylic Alkylation of Phosphonates and Phosphine Oxides with Grignard Reagents

An efficient and highly enantioselective copper‐catalyzed allylic alkylation of phosphonates and phosphine oxides with Grignard reagents and Taniaphos or phosphoramidites as chiral ligands is reported. Transformation of these products leads to a variety of new phosphorus‐containing chiral intermediates.     

Grignard additions to 2-uloses: synthesis of stereochemically pure tertiary alcohols

The addition of Grignard reagents to a number of 2-uloses has been investigated. Despite initial low diastereoselectivities it was found that tuning the ketone starting materials and studying solvent effects allowed formation of a single alcohol product.     

Fe‐Catalyzed Multicomponent Reactions: The Regioselective Alkoxy Allylation of Activated Olefins and its Application in Sequential Fe Catalysis

We present herein a versatile and broadly applicable Fe‐catalyzed regioselective alkoxy allylation of activated double bonds. Substituted allylic carbonates are converted into the corresponding σ‐enyl Fe complexes by reaction with Bu₄N[Fe(CO)₃(NO)] (TBAFe) at 30 °C. The liberated alkoxide adds to an activated double bond with the generation of a C‐nucleophile, which is trapped by the σ‐enyl Fe complex in a regioselective manner. Alternatively, the alkoxide acts as a base in deprotonating an external pronucleophile, which undergoes Michael addition. The method is characterized by a broad functional group tolerance, mild reaction conditions, low catalyst loadings, and high regioselectivities in favor of the ipso‐substitution product.     

Nickel‐Catalyzed Dimerization and Alkylarylation of 1,3‐Dienes with Alkyl Fluorides and Aryl Grignard Reagents

In the presence of a nickel catalyst, 1,3‐butadiene undergoes selective dimerization and alkylarylation with alkyl fluorides and aryl Grignard reagents to give 1,6‐octadienes with alkyl and aryl groups at the 3‐ and 8‐positions, respectively, by the consecutive formation of three carbon–carbon bonds. The formation of an anionic nickel complex plays an important role in forming C?C bonds with alkyl fluorides.     

Formation of Contiguous Quaternary and Tertiary Stereocenters by Sequential Asymmetric Conjugate Addition of Grignard Reagents to 2‐Substituted Enones and Mg–Enolate Trapping

Herein a comprehensive study is provided on the asymmetric conjugate addition (ACA) of Grignard reagents to α‐substituted cyclic enones. After the elucidation of the optimal experimental conditions, the scope of Grignard reagents and Michael acceptors was examined. Whereas secondary Grignards gave better enantioselectivities with 2‐cyclopentenones, both linear and branched Grignard reagents were tolerated for the ACA to 2‐methylcyclohexenone. The sequential ACA–enolate trapping, which leads to quaternary stereocenters, was then studied. Thus, many electrophiles have been tested, thereby giving rise to highly functionalized cyclic ketones with contiguous α‐quaternary and β‐tertiary centers. The present technique is believed to bring a new approach to versatile terpenoid‐like skeletons of bioactive natural products. Straightforward derivatizations of enantioenriched saturated cyclic ketones further support the potential of the present methodology in synthesis.     

Reactions of methylchlorodisilanes with Grignard reagents

Reactions of Cl₂MeSiSiMeCl₂ with RMgCl make it possible to obtain and isolate pure disilanes containing a smaller number of functional groups, namely, RMeClSiSiMeCl₂ (R = Ph), RMeClSiSiMeRCl (R = Prⁱ, Ph), and R₂MeSiSiMeRCl (R = Buⁱ). The reaction of Cl₂MeSiSiMeCl₂ with BuⁿMgCl is the least selective. The chlorides obtained were reduced with LiAlH₄ into the corresponding hydrides.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 954–957, May, 1995.     

Arylzinc species by microwave assisted Grignard formation-transmetallation sequence: application in the Negishi coupling

Arylmagnesium species can be efficiently generated from magnesium turnings and aryl chlorides or aryl bromides under dielectric heating conditions. Subsequent microwave assisted transmetallation using ZnCl₂-TMEDA afforded the corresponding arylzinc reagents. A sequential microwave assisted arylmagnesium formation-transmetallation-Negishi coupling protocol suitable for automated multiple parallel synthesis has been developed.