Esters reaction with organomagnesium

Table 2). Using different bases in the preparation of the phosphinites, it is possible to obtain either of the two diastereoisomers, (S p)-35 or (/ p)-35, with good diastereoselectivity [33, 34], The reaction proceeded in the presence of triethylamine in toluene solution to yield levorotatory (—)-(5p)-phosphinites 35a (or (5p)-phosphinates). Dextrorotatory phosphinates (+)-(f p)-35a (or (/ p)-phosphinates) were obtained by reaction in THF with pyridine as a base. The esters 35a,b were converted into the corresponding tertiary phosphines (or phosphine oxides) (Rp)- or (S p)-36a,b by reaction with organomagnesium in good yields (Scheme 12). The effect of the achiral base had been identified as the most important factor that determines the stereochemical outcome of the reaction. Indeed, the selectivity was reversed in the presence of pyridine. Hii et al. [34] reported that the diastereoisomeric ratio of 35 remained unchanged when the reactants were used in equimolar amounts, even at lower temperature. 

Allenyl and 1- and 2-alkynyl sulfoxides have also been prepared by reaction of organomagnesium halides with sulfinate ester 19. 1-Alkynyl p-tolyl sulfoxides were prepared in good yield from 1-alkynylmagnesium halides plus ester 19 in toluene (equation ll)63. The corresponding organolithium compound was unsatisfactory as a... 

Similar considerations apply to reactions of organomagnesium compounds with formate esters (leading to aldehydes), chloroformates or carbonates (leading to esters) or carbamoyl chlorides (leading to amides) ... 

Reactions of organomagnesium compounds with a,[3-unsaturated esters show a somewhat greater tendency to conjugate addition than reactions with a,(3-unsaturated ketones (see p. 124). However, copper(i) catalysis may be beneficial even in cases where conjugate addition is the main uncatalysed reaction [30] ... 

The usual reactions of organomagnesium compounds with esters, amides and nitriles are those described in Sections 5.3, 6.2 and 6.3. However, factors such as steric hindrance and stability of leaving group may lead to reactions resulting in overall nucleophilic displacement. Most of them are of limited applicability (see Ref. [39] for examples involving carbamate), but two warrant coverage. 

The ester moiety of methyl 2-methoxy-4-furoates underwent the usual addition reaction with Grignard reagents to provide tertiary alcohols, as exemplified in Equation (172). However, displacement of the 2-methoxy group of the corresponding 3-furoate isomers occurred under the same reaction conditions, presumably via a six-membered organomagnesium chelate, to give 2-substituted-3-furoates as the major products (Equation 173) <2003TL5781>. 

Victor Grignard assumed the existence of an unstable tetrahedral intermediate in 1901, while investigating the reaction of esters with organomagnesium reagents. The first evidence for tetrahedral intermediates in the substitution reactions of... 

There are several approaches for derivatization of squaric acid (1). The traditional major route relies on the nucleophihc reaction of the eligible esters 5 with organolithium and organomagnesium reagents their addition to 5 is known to be sufficiently selective to give 1,2-addition products 6 (4-substituted 4-hydroxy-2-cyclobutenones) from the former and... 

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