Alkylidenation of aldehydes

Reactions with other gem-diiodoalkanes under these conditions proceed in low yield however, addition of DMF (and ultrasonic irradiation) provides a very general method for alkylidenation of aldehydes with good (E)-selectivity (equation II). 

Alkylidenation of aldehydes and cyclopropanation of o jS-unsatu-rated carbonyl compounds with dibromomalonic esters... 

Dibutyl tellurium promotes alkylidenation of aldehydes by dibromomalonic esters1. 

The related reaction between carbon-carbon and carbon-oxygen double bonds is just beginning to be developed. This Wittig analog provides new routes for carbonyl alkylidenation of aldehydes, ketones and members of the carboxylic acid family. 

Knecht, M., Boland, W. (E)-Selective alkylidenation of aldehydes with reagents derived from a-acetoxy bromides, zinc and chromium trichloride. Syn/ett 1993, 837-838. 

Organozinc reagent for olefination (alkylidenation) of aldehydes, ketones, enolizable ketones, esters, in the presence of a Lewis acid. 

Alkylidenation of Aldehydes, Ketones, and Carboxylic Acid Derivatives... 

Scheme S.2S. Alkylidenation of aldehydes with RCHl2-CrCl2.

By means of these dizinc species and j8-TiClj, alkylidenation of aldehydes and ketones were examined as shown in Scheme 8.19. 

Scheme 8.44 Alkylidenation of aldehydes with RCHIj-CrClj.

Many such hydroxyquinoxalines have been made by primary synthesis (see Chapter 1) and some by hydrolysis of extranuclear halogenoquinoxalines (see Section 3.4.2) in addition, during extranuclear alkylidenation of methylquinox-alines (see Section 2.2.1.4) the intermediate secondary alcohols may sometimes be isolated, especially with heavily substituted aldehydes, when dehydration can be difficult or even impossible. ° ... 

The organotitanium compounds produced by desulfurization of the diphenyl thioacetals of aldehydes 28 with the titanocene(II) species Cp2Ti[P(OEt)3]2 29 react with carbon—carbon double bonds to form the olefin metathesis-type products. Thioacetals 28 may be transformed into terminal olefins by desulfurization with 29 under an ethene atmosphere (Scheme 14.15) [27]. This reaction is believed to proceed through a titanacyclobutane intermediate, formed by cycloaddition of the titanocene-alkylidene with ethene. 

Another method for the alkylidenation of aldonolactones uses addition of organ-ometallic reagents [78]. For example, Lin et al. [85] described an efficient route to conjugated anomeric dienes or aldehydes based on the reaction of aldono-1,4- and aldono-1,5-lactones (1, 62) with allylmagnesium chloride (Scheme 19), giving allyl hemiacetals (e.g., 63a, b). Hemiacetal can be dehydrated [e.g., with (CF3C0)20] to produce dienes 64a, b, or ozonolyzed (e.g., to give 65). 

CEJ1358> and the ruthenium mediated isomerization of double bonds (cf. Scheme 89, Section 8.11.7) <2007TL137> are recent examples of transition metal catalyzed manipulations at the side chain carbon atoms of 1,3-heterocycles. A novel side-chain addition reaction of aldehydes to 6-alkylidene-l,3-dioxin-4-ones was used for the construction of intermediates of lophotoxin <2006CJC1226>. An acid-catalyzed intramolecular cycloaddition of a hydroxy group to an alkene has been effected by the presence of an adjacent 1,3-dithiane moiety <2006TL4549>. 

CH2,CH2,C02Et. From the latter the three-carbon unit of diethyl succinate may be recognised, and the Stobbe condensation is a suitable illustration of this process. Thus the reaction of aldehydes or ketones with succinic esters in the presence of potassium t-butoxide (or with sodium hydride) gives alkylidene-succinic acid esters (25). The reaction is somewhat slower in the case of the less basic sodium ethoxide. 

The condensation products (conveniently called alkylidene dimethones) are almost insoluble in water, but can be crystallised from dilute ethanol. Dimedone is therefore a good reagent for the detection and characterisation of aldehydes. 

The alkylidene- or benzylidene-1,3-dicarbonyl compounds formed in the Knoevena-gel condensation of aldehydes or ketones with 1,3-dicarbonyls, can act not only as a... 

The yields from aldehyde alkylidenation is somewhat lower due to the reductive dimerization of aldehydes with low-valent Ti. Alkylidenation of esters is possible by the reaction of 1,1 -dibromoalkane. TiCU and Zn in the presence of TMEDA to give (Z) vinyl ethers [60], Cyclic vinyl ethers are prepared from unsaturated esters in two steps. The first step is formation of the acyclic enol ethers using a stoichiometric amount of the Ti reagent, and the second step is ring-closing alkene metathesis catalysed by Mo complex 19. Thus the benzofiiran moiety of sophora compound I (199, R = H) was synthesized by the carbonyl alkenation of ester in 197 with the Ti reagent prepared in situ, and the subsequent catalytic RCM of the resulting enol ether 198 catalysed by 19 [61]. 

Addition of Aldehydes to Nitroolefins and Alkylidene Malonates 2.3.4.1 Aminopyrrolidine Catalysts... 

C-Alkylpyrazines undergo extranuclear alkylidenation by aldehydes (or ketones,) with or without isolation of the intermediate (hydroxyalkyl)pyrazines. Several procedures are illustrated in the following examples ... 

Various other [3 + 2] cycloadditions, affording chiral, anellated C6o derivatives with stereogenic centers in the addends are reported in literature. The products were generally obtained as racemates and resulted from reaction of buckminsterfullerene with species like 2,3-disubstituted 2//-azirincs (via nitrile ylides [under direct irradiation] or via 2-azaallenyl radical cations [sensitization by photoinduced electron transfer]),365 1-substituted 5-diazopentane-1,4-diones (via cyclic carbonyl ylides),366 7-alkylidene-2,3-diazabicyclo[2.2.1] hept-2-ene (via a diradicaloid trimethylenemethane derivative),367 1-benzylpy-razolidine-3-ones in the presence of aldehydes (via pyrazolidinium ylides),368 2-trifluoromethyl-2,5-dihydro-l,3-oxazol-5-ones (via nitrile ylides),369 nitro-alkanes in the presence of triethylamine and trimethylsilyl chloride (via N-silyloxynitrones),370 or dv-HOCH2 CH=C H C H 2 OCO 2 H( in the presence of... 

Scheme 5. General alkylidenation of esters to enol ethers 9 and synthesis of disubstituted ( )-alkenes 10 from aldehydes and chromium(II) reagents according to Takai and Utimoto.

Under the reaction conditions for alkylidenation, compounds containing the following functional groups were found to be stable trimethylsilyl ethers of alcohols, olefins, primary alkyl iodides, and ethylene acetals of aldehydes. 

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