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Aldehydes cycloisomerization

The Alder-ene cyclization of allylic silyl ethers represents a clever use of cycloisomerization chemistry, as the enol ether products can be easily unmasked to yield aldehydes. Palladium-catalyzed cycloisomerization of 1,6- and 1,7-enynes containing an allylic oxygen most often gives rise to 1,3-dienes (see Section 10.12.4.1). However, enynes of type 63 underwent facile Alder-ene cyclization to the corresponding five- or six-membered rings (Equation (40)) using both [CpRu(MeCN)3]PF6 41 and the Cp analog ([Cp Ru(MeCN)3]PF6, 64).53... [Pg.573]

Marshall et al. noted that under the catalysis of Ag+ or Rh+, 1,2-allenyl ketone or aldehyde 417 may undergo cycloisomerization to afford furans 418. The reaction proceeded via the interaction of Ag+ or Rh+ with the relatively electron-rich C=C bond in the allene moiety followed by nucleophilic attack of the carbonyl oxygen [187]. Through a labeling study, it was found that the reaction proceeds by the mechanism shown in Scheme 10.162 [188]. [Pg.660]

Terminal alkynals (113) of appropriate length (n = 1, 2) and substitution [X = C(C02-Me)2, C(CH2OR)2, NTs, and others] have been cyclized with decarbonylation to cycloalkenes (114), using a ruthenium(I) catalyst.348 In some cases, cycloisomerization to give conjugated aldehyde occurred. Both processes are believed to involve catalytic ruthenium vinylidenes. [Pg.43]

Furthermore, the choice of enyne substrates can lead to cyclized products that contain other functionalities than dienes. Very recently, Muller and Kressierer [148] have shown that yne allyl alcohols 200 can be rapidly cyclo-isomerized by a Pd2dba3-W-acetyl phenyl alanine catalyst system to furnish heterocyclic enals 202 in excellent yields (Scheme 82). The intermediate product of the enyne cycloisomerization in this case is the enol 201, which rapidly tautomerizes to the aldehyde 202. [Pg.193]

Platinum(ll)-catalyzed carbocyclization of a.ty-enynes has been intensively researched lately. For instance, 2-disubstituted l-en-6-ynes react with methanol in the presence of PtCl2 as catalyst to form carbocycles with exocyclic aUcenes. The analogous reactions of 3-allyl propargyl ether or 3-allyl propargyl tosylamine in water using the same catalysts will generate cyclopropyl aldehydes besides the product of cycloisomerization (Scheme 82). The coordination of the... [Pg.3929]

Preparation of an useful synthon, the cyclic carbamate of L-daunosaminal (104), was achieved by sequential catalytic transformations of a key intermediate. Suitably protected propargyl diol 101, which was obtained by diastereoselective addition of allenyl stannate 99 to 0-benzyl (S)-lactyl aldehyde 100, was transformed as depicted in Scheme 18. Cycloisomerization to 3-deoxyglycal 103 was achieved by irradiation in the presence of tungsten hexacarbonyl, and subsequent nitrene insertion was catalyzed by rhodium acetate. Overall yield of the bicyclic daunosaminal (104) derivative from lactic acid derivative amounted to 44% [78]. [Pg.268]

A double cyclization of an aldehyde enol to the methylene malonate, followed by a cycloisomerization onto the triple bond, leads to a bicyclo[5.3.0] decane of a tris-norguaiane (Scheme 10) [45]. [Pg.432]

A gold(III)-catalyzed multicomponent coupling/cycloisomerization reaction of heteroaryl aldehydes, amines, and alkynes imder solvent-free conditions or in water has been developed as shown in Scheme 8.2 [2]. This methodology provides rapid access to substituted aminoindolizines with high atom economy and high catalytic efficiency. Especially, the coupling of enantiomerically enriched amino acid derivatives produces the corresponding A/ -indolizine-incorporated amino acid derivatives without loss of enantiomeric purity. [Pg.233]

Multicomponent sequential transition-metal-catalyzed reactions were accomplished by the group of Muller. Their approach involves cycloisomerizations or combinations of a Heck reaction and an insertion or allylic substitution reaction, yielding an intermediate from which by P-H-elimination an aldehyde is generated, which reacts with an amine to give an imine, which in turn is reduced or otherwise modified. This conceptually challenging approach allows the experimentally remarkably facile generation of a variety of compounds of interest in medicinal chemistry. [Pg.236]

By the choice of the enyne substrates, the obtained cyclized products might contain functionalities other than dienes. The unusual catalyst combination of a Pd precatalyst and formic acid enables sequential catalysis initiated by cycloisomerization in a very peculiar way. Kressierer and Muller [16] demonstrated in several cases that the palladium(0)-catalyzed Alder-ene reaction of a-alkynyl M-allyl alcohols 7 furnishes cyclic y,5-enals 8 as a consequence of the in situ enol-aldehyde tautomerism (Scheme 12.2). [Pg.257]

The newly generated aldehyde functionality was reacted in consecutive carbonyl transformations, such as cycloisomerization-Wittig [16] and cycloisomerization-Leuckart-Wallach [17] one-pot sequences to give five-membered carbo- and heterocycles with densely functionalized side chains. [Pg.258]

The Rh-BINAP-catalyzed intramolecular Alder-ene cycloisomerization is very rapid and, therefore, sequentially Rh-catalyzed sequences for the efficient enantioselective generation of five-membered carbo- and heterocycles were envisioned. Korber et al. [21] reported the enantioselective rhodium-catalyzed cycloisomerization of alkyl and (hetero)aryl alkynyl allyl alcohols for the generation of aldehyde-bearing chiral 4-alkyl 3-alkylidene THFs and tetrahydro-furanones, which were converted into a,P-unsaturated carbonyl side chains in a one-pot manner via a concluding Wittig olefination in good yields. [Pg.260]

Kummeter et al. [34] successfully employed this type of Alder-ene cycloisomerization as an entry to a sequentially Ir-catalyzed cycloisomerization-Murahashi reaction sequence in a one-pot manner, where the intermediate aldehyde arising from the Alder-ene tautomerization step was condensed with cyano acetic esters without addition of acids or bases, furnishing five-membered heterocycles 19 with super-Michael acceptors in the side chain (Scheme 12.10). [Pg.262]

As in (3a), the formation of the propargylated 2-pyridyl system can become part of a sequential C coupling/cycloisomerization strategy. Thus, pyridine-2-aldehyde, secondary amines, and terminal alkynes participate in an Au-catalyzed multi-component domino process to give 1-aminosubstituted indolizines 32 [225] ... [Pg.156]

In the presence of an aldehyde (or ketone) such as 36, the cycloisomerization of 1,6-enyne 37 evolves toward the formation of 2-oxabicyclo[3.1.0]hexanes 42 (Scheme 5.14) [63]. According to the authors, the 5-exo-dig carbenoid intermediate... [Pg.124]

Scheme 34 Ru-catalyzed decarbonylative cyclization of terminal alkynals to cycloalkenes and cycloisomerization to cyclic a,p-unsaturated aldehydes... Scheme 34 Ru-catalyzed decarbonylative cyclization of terminal alkynals to cycloalkenes and cycloisomerization to cyclic a,p-unsaturated aldehydes...

See other pages where Aldehydes cycloisomerization is mentioned: [Pg.571]    [Pg.571]    [Pg.459]    [Pg.182]    [Pg.156]    [Pg.279]    [Pg.206]    [Pg.241]    [Pg.1620]    [Pg.555]    [Pg.36]    [Pg.398]    [Pg.377]    [Pg.467]    [Pg.478]    [Pg.100]    [Pg.95]    [Pg.74]    [Pg.377]    [Pg.467]    [Pg.478]    [Pg.1620]    [Pg.387]   
See also in sourсe #XX -- [ Pg.43 ]




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Cycloisomerism

Cycloisomerization

Cycloisomerizations

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