Structures,stabilities, and energies of isomerization of α-cyano and α-isocyano carbanions

Ab initio STO -3G calculations show that α-cyano- and α-isocyano-substitution on carbanions produce a significant approximately equal stabilization of these charged species. Evidence is presented which suggests that the mechanism of such stabilization is qualitatively different for the cyano and isocyano substituents. The former appears to act through an electron delocalization process while the latter may operate by an inductive effect.     

Chlorination of α-sulfonyl carbanions with hexachloroethane: A novel preparation of α-halosulfones

The cyclic sulfones1,2, and3 are lithiated in benzene with n-butyllithium. Lithiation is demonstrated to lead to α-mono, α,α′-di and/or α,α-di and α,α,α′ trimetallation. The lithiated sulfones are chlorinated with hexachloroethane (HCE). Some mechanistic aspects of the reaction of the lithiosulfones with vicinal dihalides are discussed.     

Coupling reaction of poly(α-methylstyryl) anion with (MMA–α-methylstyrene) block copolymer

(MMA–α-methylstyrene)block copolymer was reacted with poly(α-methylstyryl)anion at ?78°C in a mixture of good tetrahydrofuran (THF) and poor methylcyclohexane solvents. The reaction conditions were chosen so as to produce graft copolymers made up of a backbone (AB-type block copolymer) and a single branched chain (1:2 graft copolymer). Gel permeation chromatograph (GPC), osmotic pressure measurement, and elemental analysis were used for the characterization of 1:2 graft copolymer. It appeared that poly(α-methylstyryl)anion reacted with the end pendant groups located farthest away from the branched point of AB-type block copolymer, when the dimensions of AB-type block copolymer molecule are small.     

The aging of living α-methylstyryl oligomers. I. The kinetics of aging

Solutions of living oligomers of α-methylstyrene in THF age in two ways. In “decay” the UV-visible absorption of the anion slowly disappears but in “transformation” the peak at 340 nm is replaced by a new one at 430 nm. Decay follows first-order kinetics, while transformation depends upon a photochemical process and requires the presence of excess monomer. This monomer is consumed in a second-order reaction to produce an intermediate from which new anions are formed.     

The aging of living α-methylstyryl oligomers. II. The mechanism of aging

The living anions of oligomeric α-methalystyrene in THF transform to a new anion in the presence of excess monomer and UV light. Kinetic results have demonstrated that one step in this process is the second-order disappearance of monomer to form a dimeric intermediate. We have attempted to prepare this intermediate. Contrary to other reports, no hydrogen was liberated on terminating the reactions mixture with water, and an oily liquid which was identified as 1-methyl-1,3-diphenyl-cyclopentane was isolated. However, this is not the intermediate; the true intermediate is 2,5-diphenylhex-1-ene and under the conditions of the reaction the former compound is formed from this by a cyclization reaction.     

A novel synthesis of α-hydroxy- and α,α′-dihydroxyketone from α-iodo and α,α′-diiodo ketone using photoirradiation

A novel reaction of α-iodo ketone (α-iodocycloalkanone, α-iodo-β-alkoxy ester, and α-iodoacyclicketone) with irradiation under a high-pressure mercury lamp gave the corresponding α-hydroxyketone in good yields. In the case of α,α′-diiodo ketone, α,α′-dihydroxyketone which little has been reported until now was obtained. This reaction affords a new, clean and convenient synthetic method for α-hydroxy- and α,α′-dihydroxyketone.     

Microwave-assisted synthesis of α-hydroxy ketone and α-diketone and pyrazine derivatives from α-halo and α,α′-dibromo ketone

A novel reaction of α-halo ketone (α-bromo and α-chloro ketone) with irradiation under microwave gave the corresponding α-hydroxyketone and pyrazine derivative in good yields. In the case of α,α′-dibromo ketone, α-diketone was obtained. This reaction affords a new, clean and convenient synthetic method for α-hydroxyketone, α-diketone, α-chloro ketone and pyrazine derivative.     

New synthesis of α-nitroalkyl- and α-nitroaralkylcarboxylic esters from α-nitroalkyl- and α-nitroaralkyl-2-oxazolines

2-Nitroalkyl- and 2-nitroaralkyl-2-oxazolines are readily converted, in one step, to α-nitroalkyl- and α-nitroaralkylcarboxylic esters on treatment with the appropriate alcohol and trifluoroacetic acid (TFA). The initial products of the ring cleavage are the TFA salts of the ammonioalkyl esters of α-nitroalkyl- and α-nitroaralkylcarboxylic acids. These salts undergo facile transesterification to the α-nitrocarboxylic esters on refluxing with the appropriate alcohol.     

Reaction of α-keto hydrazonyl bromide with carbanions of some active methylene compounds

Treatment of 1-phenyl-2-bromo-2-arylhydrazonoethanone (VII) with sodium etiolates of 2,4-pentanedione, 1-phenyl-1,3-butanedione, dibenzoylmethane, ethyl benzoylacetate, acetoaceta-nilide, and of benzoylacetanilide in ethanol afforded the substituted pyrazoles, VIII-XIII, respectively. The results show that VII, unlike 1-phenyl-2-bromo-2-hydroximinoethanone (V), is not easily deprotonated by carbanions; and that its reactions with β-diketones, β-keto esters, and β-keto amides follow one and the same mechanism. The structures of the products (VIII-XIII) were inferred from their elemental analyses and spectral data.     

Preparation of α-Bromo- and α-Chlorocarboxylic Acids from α-Amino Acids

Diazotization of α-amino acids in 48:52 (w/w) hydrogen fluoride/pyridine along with excess of potassium halide results in the corresponding α-halocarboxylic acids in good to excellent yields (Table 1 and 2).