Of activated methylene group

Compounds of the type HC=C—CH=CHXR are not involved in a primary reaction with weak nucleophiles such as CH acids meanwhile, a final (secondary) cyclization with participation of active methylene groups happens to be feasible. Evidently, in most cases the energy gain in the heteroaromatic system realization is the decisive factor (81UK1252). 

The oxidation of active methylene groups by periodate both in acyclic... 

Direct sulphanylation of activated methylene groups to form methyl thioethers is possible under basic conditions, when the stabilized carbanion reacts with 5-methyl methanethiosulphonate. The reaction has been applied successfully in, for example, reactions with p-keto sulphoxides [59] and a-sulphonyl acetic esters [60] (Scheme 4.13). 

The reaction of activated methylene groups with tosyl azide to yield the corresponding diazo derivatives proceeds in high yield [23]. The phase-transfer catalysed reaction is sensitive to the strength of base used the reaction of acetoacetic esters requires relatively mild conditions, otherwise diazoacetic esters are produced (Table 5.41). 

Periodate oxidation of activated methylene groups (ArCHRC02H -> ArCOR)... 

For solution phase photopolymerization, photosensitive solutions must be prepared immediately before use. In film-based compositions, stability and sensitivity are lost in 2-5 days (compare Tables 6, 10). The lack of stability is directly related to the nature of the activator, although not in a way that necessarily parallels photosensitivity. The photoactivated reaction, dye-activator redox chemistry, is a go/no-go process and does not contribute to the dark reaction. Rather, dark reactions are in general a consequence of the basicity of most common activators, for example, amines, sulfinates, or enolates. Deprotonation of active methylene groups on some dyes (e.g.,... 

The analogous oxidation of active methylene groups formed during the oxidation of a variety of carbohydrates by periodate has been considered in detail.22... 

The prerequisite 1,5-dicarbonyl compounds and their equivalents can be formed in situ by a Michael addition of activated methylene groups onto O Ji-unsaturated systems <1996CHEC-II>. In this manner, 5-alkylidene-2-thioxo-dihydropyrimidincM,6(l //,5//)-dione 84 reacts with ethyl 3-oxobutanoate under microwave irradiation to from the intermediate 1,5-dicarbonyl compound 85, which spontaneously cyclize to afford the corresponding 4//-pyrans in high yield (Scheme 28) <2003SC3747>. 

Approaches that represent a type (ii) synthesis of 277-pyran-2-ones include the self-condensation of 1,3-dicarbonyl compounds, the reaction of cyclopropanones with pyridinium enolbetaines and the reaction of activated methylene groups with acetylenic esters <1984CHEC, 1996CHEC-II>. 4-Perfluoroalkyl-6-aryl-pyran-2-ones are formed by the reaction of the phosphonium salts 631 with 2-perfluoroalkynoates (Equation 254) <1999JFC(95)135, 1998JFC(91)99>. Dimedone reacts with dimethyl acetylenedicarboxylate to afford the pyran-2-one 632 in excellent yield (Equation 255) <2003PS2627>. 

Reactions of Active Methylene Groups in Side Chains... 

Abramovitch, R.A., Shi, Q., and Bogdal, D. 1995. Microwave-assisted alkylations of activated methylene groups. Synthetic Communications, 25 1-8. 

Selenium dioxide (SeOi) oxidation Selenium dioxide is an excellent oxidizing agent for the oxidation of allylic and benzylic C-H fragments to allylic or benzylic alcohol. It also oxidizes the aldehydes and ketones to 1,2-dicarbonyl compounds (i.e. oxidation of active methylene groups to carbonyl groups). 

OXIDATION WITH p-NITROSODIMETHYLANILINE Oxidation of Activated Methylene Group to Carbonyl [986]... 

An interesting application of the method of nitration of active methylene group is the nitration of methyl group in a- and 7-picoline [103], for example ... 

Recently. Petrov and co-workers also [121, 122) published a number of papers on the nitration of active methylene groups with nitrate esters. 

Riley oxidations. Oxidations of organic compounds with selenium dioxide, e.g., the oxidation of active methylene groups to carbonyl groups. 

The following regularities have been observed in allylic bromination of mono-, di-, and alicyclic olefins by NBS.352,354 In absence of activation methylene groups are brominated more easily than methyl groups, and these somewhat more easily than methine groups. Straight-chain and branched-chain olefins are brominated by NBS only once at each allyl position two bromine... 

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