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Aldehydes alkylidene transfer

Finally, aldehydes have also been reported to serve as alkylidene transfer reagents.93 Examples of these further cyclopropanation procedures are summarized in Table 6. [Pg.976]

In 1973 Mukaiyama, Tyrlik, and McMurry discovered a remarkably simple reaction that couples aldehydes or keto compounds reductively to olefins [1, 2]. This methodology following eq. (1) differs from that of Section 3.2.10 in that no extra methylene or alkylidene transfer reagent is required. The stereochemistry of the product depends on the nature of the substituents R and whether an open-chain or a cyclic olefin results. [Pg.1093]

If competitive aldehydes or ketones are used, preferred or exclusive formation of the sterically least hindered alkylidene dipyrazole is observed.[32] If A -carbonyldipyrazole is heated at 190 °C a pyrazole-transfer reaction also occurs to give tetrapyrazole-l-yl-methane in 50% yield.[33]... [Pg.392]

The Williamson ether synthesis remains the most practical method for the preparation of tetrahydrofurans, as can be exemplified by the two examples shown in the following schemes. A simple synthesis of 2-substituted tetrahydrofuran-3-carbonitriles 84 is achieved by generating the alkoxide under a phase transfer condition via reaction between 4-chlorobutyronitrile and non-enolizable aldehydes <00SL1773>. A synthesis of 2-alkylidene-tetrahydrofuran 85 was recorded, in which a dianion can be generated through treatment of the amide shown below with an excess of LDA, and is followed by addition of l-bromo-2-chloroethane. In this way, the more basic y-carbon is alkylated and leads eventually to the nucleophilic cyclization <00SL743>. [Pg.148]

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... [Pg.88]

An approach to the problem is summarized in eq. (3). Aldehydes are subject to catalytic olefination when certain aliphatic diazoalkanes are used as alkylidene group transfer reagents phosphines are necessary to carry off the 0x0 group. [Pg.1079]

It was noted above that the photolysis of indole and aldehydes in the solid state leads to diindolymethanes by a mechanism postulated to involve an oxetane intermediate (Scheme 14). The reaction also proceeds when aromatic aldehydes and indole or 2-methylindole are irradiated with UV light in acetonitrile solution (Scheme 28) [61]. Under these circumstances, it has been proposed that light-induced electron transfer from the indole to the aldehyde yields a ketyl radical anion and the indole radical cation. Proton transfers, coupling, and elimination of water can then yield an electrophilic alkylidene indolenine 65 which can react with indole thermally to give the observed product. [Pg.255]

Among asymmetric version of barium-catalyzed aldol reactions, the direct aldol reaction of y3,y-unsaturated esters with aldehydes is promising due to the DYKAT (dynamic kinetic asymmetric transformation). Shibasaki and coworkers (147) established an optimized catalyst system for the DYKAT involving aldol/retro-aldol reaction, that a Ba(0-iPr)2/BIN0L mixture gave excellent enan-tioinduction and conversion (Scheme 32). a-Alkylidene-y3-hydroxy esters were obtained under proton-transfer conditions via DYKAT in 87-99% ee. [Pg.2224]

A limited number of ylides are available which allow the transfer of more complex alkylidene units, such as an isopropylidene group (entries 9 and 10) or a cyclopropylidene group (entries 11 and 12). The oxaspiropentanes formed by reaction of aldehydes and ketones with diphenylsulfonium cyclopropylide are useful intermediates in a number of transformations such as acid-catalyzed isomerization to cyclobutanones. [Pg.82]

The second method of controlling the polymerization of these systems was the addition of phosphine, an inhibitor, to the system that stabilized the intermediate, deaeased the reactivity of the chain end, and resulted in much narrower polydispersity. The additives appeared to operate by the reversible termination principle that is the basis for atom transfer radical polymerization (ATRP). As was the case with the Tebbe systems, the trmgsten alkylidenes reacted cleanly with aldehydes or ketones. Consequently, the living systems could be terminated by the addition of an aldehyde or ketone. [Pg.23]


See other pages where Aldehydes alkylidene transfer is mentioned: [Pg.13]    [Pg.13]    [Pg.994]    [Pg.294]    [Pg.1125]    [Pg.1125]    [Pg.240]    [Pg.82]    [Pg.643]    [Pg.807]    [Pg.808]    [Pg.1078]    [Pg.1079]    [Pg.1491]    [Pg.807]    [Pg.808]    [Pg.412]    [Pg.41]    [Pg.299]    [Pg.807]    [Pg.808]    [Pg.218]    [Pg.475]    [Pg.14]    [Pg.634]   
See also in sourсe #XX -- [ Pg.976 ]




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