Alkyne derivatives formate anions

The first complexes of a-keto ylides and group 5 early transition metals have only recently been obtained by reaction of Nb(III) derivatives [[NbCl3(dme) (R C=CR")] with 25 (R = thiazolyl) (Scheme 16). The chelation of the ylide occurs through an N,0-coordination to the metal center and in presence of MeLi a deprotonation of a phenyl ring takes place with the loss of alkyne, leading to the formation of a new orfho-metallated binuclear compound 32. The two ylides involved in the complexation behave as tridentate anionic ligands and are mutually in a trans disposition in order to minimize the steric hindrance [71,72]. Another binuclear niobium complex 33 has been obtained from 25 (R = Me, Ph) with this time an 0-coordinated a-keto ylide [68]. 

Acyl halides and alkynes also give lactones upon reaction with Ni(CO)4 in an aqueous acetone medium. The result in this system is typically a 3,y-unsaturated lactone, formed together with some product derived from condensation with molecules of solvent (equation 18). Lactones are also formed in low yield as byproducts from the reactions of acylnickel carbonyl anions (derived from addition of RLi to Ni(CO)4) with terminal alkynes at -30 A single example of y-aminolactone formation is reported from 2-butyne, CO and diethylamine, catalyzed by (Et2NH)2NiBr2. ... 

Few examples of functionalization on the benzene ring of benzisothiazole have been reported (see Section 4.05.7.2). Studies on the reactivity of unsaturated chains in cycloaddition reactions have been reported (see Section 4.05.7.3). The high reactivity of 4-vinylisothiazolin-3-one A-oxides in Diels-Alder cycloadditions, both as diene and dienophile, is illustrated by their tendency to dimerize. 5-Vinylisothiazole A,A-dioxides react at the vinyl function with different 1,3-dipoles. Isothiazolo-3-sulfolenes 265 give an o-quinodimethane which can be trapped with a dienophile. Different isothiazole derivatives substituted with a carbon chain functionalized with heteroatoms have been prepared as ligands for the formation of complexes. 3-Oxocamphorsulfonimide reacts with the anion of alkynes and several studies on the reactivity of the products with electrophiles are reported. 

In an analogous manner, treatment of 4-(2-haloethyl)-phenols and -l-naphthols " with bases produces spiro[2.5]octa-4,7-dien-6-ones and their benzo analogues, respectively. The basic treatments of jS-oxiranyl ketones , esters (equation 13) , nitriles , sulfones and alkynes affords 2-(hydroxymethyl) cyclopropyl derivatives, usually as the sole cyclization product. The cyclization occurs regiospecifically by the intramolecular attack of the anion on the y-carbon in the oxirane ring. Attack of the anion on the 5-carbon in the oxirane, which should lead to the formation of cyclobutanols, usually does not take... 

The reaction of carbon nucleophiles with ketones or aldehydes proceeds by acyl addition, as described in Chapter 18. The reaction of carbon nucleophiles with acid derivatives proceeds by acyl substitution, as described in Chapter 20. Carbon nucleophiles included cyanide, alkyne anions, Grignard reagents, organolithium reagents, and organocuprates. Alkyne anions are formed by an acid-base reaction with terminal alkynes (RC=C-H RCsCr). In this latter transformation, it is clear that formation of the alkyne anion relies on the fact that a terminal alkyne is a weak carbon acid. Other carbon acids specifically involve the proton on an a-carbon in aldehydes, ketones, or esters. With a siiitable base, these carbonyl compounds generate a new type of carbon nucleophile called an enolate anion. 

P-Ketophosphonates are valuable intermediates in the realm of Homer-Emmons alkenation methodology. Acyclic variants are difficult to obtain from enol phosphates due to competing alkyne and allene formation. One solution utilized the dianion derived from a-bromo ketones and trapping with diethyl phosphorochloridate however, only moderate yields of P-keto phosphonates were reported. The most efficient procedure utilizes the anion derived from dialkyl methylphosphonate, addition to an aldehyde, followed by oxidation (eq 8). ... 

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