Ethers homopropargylic

In the case of nonracemic homopropargylic ether 17, hydrozirconation/carbonylation was followed by exposure of the intermediate to molecular iodine (Scheme 4.12) [39]. The ( )- and (Z)-forms of the acyl iodide presumed to be formed in situ were seemingly in equilibrium under the reaction conditions and intramolecular attack followed by dealkylation afforded (S)-(+)-parasorbic acid. 

Allenylsilanes react with acetals to afford homopropargylic ethers (Table 9.37) [61]. These reactions are promoted by silyl and carbocation species. A variation of this conversion involves in situ formation of the acetal from an aldehyde and Me3SiOMe (Eq. 9.55). The success of this method indicates that conversion of the aldehyde to the acetal and its subsequent reaction with the silane must be faster than direct reaction of the aldehyde with the silane. 

Amines have also been applied as nucleophiles.f Under the catalysis of the palladium, the o-iodobenzyl homopropargyl ether 52 formed the seven-membered ring vinyl-palladium intermediate 53, which subsequently reacted with 1,2-propadiene in the presence of a secondary amine to eventually afford 54 (Scheme 20). 

Intramolecular additions of alcohols or amines to olefins are recognized as useful methods to provide heterocyclic compounds. Kozmin and Zhang have achieved a gold-catalyzed synthesis of heterobicyclic alkenes by double cyclization of alcohols or sulfonamides which have a 1,5-enyne moiety [175]. As a typical example, unsaturated alcohol (95) is smoothly converted to 6-oxabicyclo[3.2.1]octane (96) in 90% yield using a 5 mol% of AuCls catalyst (Scheme 18.34). Cyclic ethers are also available from homopropargylic ethers with pendant alcohols through gold-catalyzed... 

Scheme 42/ A route to homopropargylic ethers from silylallenes has been mentioned earlier (c/. Scheme 23). ...

SCHEME 4.31 Gold-catalyzed tetrahydropyran synthesis from homopropargylic ethers. 

Homopropargyl ether 87 underwent a multicomponent coupling reaction to give cyclopropylalkylamides 88 in good yields by successive treatment with Cp2ZrHCl, MeaZn, imine, and CH2I2 (Scheme 1.47) [81]. 

The gold(I)-catalysed oxidative rearrangement of propargyl alcohols has been reported as a selective route to 1,3-diketones (Scheme 123). a,j0-Unsaturated carbonyl compounds have been reported to be formed from gold-catalysed oxidative rearrangement of homopropargylic ether with a gold carbenoid and oxonium ylide proposed as intermediates (Scheme 124). ... 

Additionally, homopropargylic ethers with pendant nucleophiles, when subjected to gold catalysts in an aqueous solvent, provide heterocychc ketones (5- and 6-membered rings) (Scheme 17) [136,137]. This method was applied to the formation of piperidines... 

Propargylic ethers undergo directed lithiation and subsequent transmetallation to afford oxygenated allenyl titanium reagents. Subsequent addition of aldehydes gives rise to various homopropargylic alcohol adducts as mixtures favoring the anti dia-stereomers (Tables 9.18 and 9.19) [29, 30]... 

In the presence of TiCl4, 1,2-allenylsilanes can react with aldehydes, ketones or acetals to give homopropargyl alcohols or ethers [33],... 

Chiral allenylmetal compounds provide convenient access to enantioenriched homopropargylic alcohols through Se2 additions to aldehydes. The syn adducts can be obtained through addition of allenyl tributylstannanes in the presence of stoichiometric boron trifluoride etherate (BF3-OEt2). The use of allenylmetal halides derivatives of Sn, Zn, and In lead to the anti diastereomers. The former additions proceed through an acyclic transition slate whereas the latter are thought to involve a cyclic transition state, thus accounting for the difference in diastereoselectivity. 

Allyltributyltin, 10 Vinyltrimethylsilane, 343 Homoallylic ethers Allyltrimethylsilane, 11 Crotyltrimethylsilane, 86 Trityl perchlorate, 339 Homopropargylic alcohols Allenylboronic acid, 36 D imethoxy [ 1 -trimethylsilyl-1,2-buta-dienyljborane, 218 Lithium acetylide, 44 Triisopropoxy[l-(trimethylsilyl)-l,2-buta-dienyl]titanium, 218 Hydroperoxides Oxygen, singlet, 228 Hydroxy acids a-Hydroxy acids... 

Zn, BrCH2CH2Br, CuBr, LiBr, EtOH (propargylic and homopropargylic alcohol and amine, propargyhc ether, enyne, diyne)... 

Dihydropyrans. The silyl ethers of homopropargyl alcohols in the presence of TiCl4 condense with aldehydes to form dihydropyrans. This reaction is highly dependent on the substituents of the silyl group, with best results obtained with the bis-silyl ether (1) of 4-pentynol-2. Use of A1C13 as catalyst or of the free alcohol results in at least three acyclic products. 

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