Organolithium reagents acylation

Alkyltriphenylphosphonium halides are only weakly acidic, and a strong base must be used for deprotonation. Possibilities include organolithium reagents, the anion of dimethyl sulfoxide, and amide ion or substituted amide anions, such as LDA or NaHMDS. The ylides are not normally isolated, so the reaction is carried out either with the carbonyl compound present or with it added immediately after ylide formation. Ylides with nonpolar substituents, e.g., R = H, alkyl, aryl, are quite reactive toward both ketones and aldehydes. Ylides having an a-EWG substituent, such as alkoxycarbonyl or acyl, are less reactive and are called stabilized ylides. 

Acyliron complexes have found many applications in organic synthesis [40]. Usually they are prepared by acylation of [CpFe(CO)2] with acyl chlorides or mixed anhydrides (Scheme 1.13). This procedure affords alkyl, aryl and a,P-unsaturated acyliron complexes. Alternatively, acyliron complexes can be obtained by treatment of [Fe(C5Me5)(CO)4]+ with organolithium reagents, a,P-Unsaturated acyliron complexes can be obtained by reaction of the same reagent with 2-alkyn-l-ols. Deprotonation of acyliron complexes with butyllithium generates the corresponding enolates, which can be functionalized by reaction with various electrophiles [40]. 

Lack of conjugation leads to increased reactivity, and N-acyl aziridines are useful in synthesis because they react with organo-lithium reagents only once to give ketones. No further reactions of the product ketone occur because the N-acyl aziridine is reactive enough to compete with it for the organolithium reagent. 

Section I)13. In the case of the carboxylic anion, the lithiation of acyclic and cyclic orthoth-ioesters allows the preparation of intermediates XII12. All these stabilized organolithium reagents have been widely used in organic synthesis and in this section their application as acylating agents by this defensive strategy will be mainly considered. 

As further illustrated in Scheme 2, the 1-methyl- and 1,3,3-trimethylcyclopropene are rapidly metallated with organolithium reagents in ether to afford stable solutions of the 1-lithiocyclopropenes (18) In comparison, solutions of the metallocyclopropenes (16) are significantly less stable and even at — 40°C are observed to degrade slowly to a mixture of dimeric and trimeric products apparently formed by nucleophilic addition of 16 to the highly reactive cyclopropene n system L Alkylation of 18 (R=H or Me) with methyl iodide produced 1,2-dimethyl- and 1,2,3,3-tetramethylcyclopropene . The trimethyl derivative 18 (R = Me) has also been carbonated and acylated to afford the corresponding 2,3,3-trimethylcyclopropene carboxylic acid, methyl ketone and carboxaldehyde. 

The introduction of the trifluoroacetyl moiety into aromatics and heteroaromatics has been generally realized by Friedel-Crafts acylation and by reaction of organomagnesium or organolithium reagents with ethyl tiifluoroacetate, trifluoroacetic acid, or its salts [4-10 and Refs, therein]. 

---