Alcohols alkynyl

The addition of lithium acetylides can also be carried out enantioselectively in the presence of 22-24 ]vjucieophiiic addition of the unsubstituted lithium acetylide led to the alkynyl alcohol with lower enantioselectivity than the addition ofsilyl-substituted acetylides. The trimethylsilyl substituted acetylides gave the best results. 

Optically active alkynyl alcohols can, however, be conveniently prepared by the addition of dialkylzinc reagents of alkynyl aldehydes catalyzed by the chiral ligand (S)-l-methyl-a,a-diphenyl-2-pyrrolidine methanol33-34. 

There is no way in which dehydration of alcohols can be used to prepare triple bonds gem-diols and vinylic alcohols are not normally stable compounds and vic-diols give either conjugated dienes or lose only 1 mol of water to give an aldehyde or ketone. Dienes can be prepared, however, by heating alkynyl alcohols with triphenyl phosphine. ... 

TTie solvolysis of propargylic substrates (199) and formation of alkynylcarbonium ions (200) has been extensively investigated. Particularly good evidence for the formation of alkynylcarbonium ions comes from the nuclear magnetic resonance spectra of alkynyl alcohols in strong acid media (200, 201). The downfield shifts of 4ppm for the proton of HC=C— and 1 ppm for CH3C=C- relative to their neutral precursors is indicative of carbonium-ion formation and shows the importance of the allenyl resonance contribution. 

The intramolecular addition of the O-H bond to alkynes catalyzed by palladium complexes has been developed by K. Utimoto et al. (Eq. 6.59) [104]. An alkynyl alcohol can be converted to a cyclic alkenyl ether in the presence of a catalytic amount of [PdCl2(PhCN)2 or [PdCl2(MeCN)2] in ether or THE at room temperature. When the reaction was carried out in MeCN-H20 under reflux in the presence of a catalytic amount of PdCl2, hydration of the acetylenic alcohol occurred and the ketoalcohol was obtained in good yield instead. 

A complementary route to carbohydrate-based oxepines was developed by the McDonald group.67 It is based on the endo-selective cycloisomerization of alkynyl alcohols in the presence of molybdenum or tungsten catalysts to give the cyclic enol... 

SCHEME 23. c m/o-Selective cycloisomerization of alkynyl alcohols in the presence of molybdenum or tungsten catalysts. 

Entry Alkynyl alcohol Endocyclic enol ether Isolated yield Reference... 

Asymmetric synthesis of stavudine and cordycepin, anti-HIV agents, and several 3 -amino-3 -deoxy-P-nudeosides was achieved utilizing this cycloisomerization of 3-butynols to dihydrofuran derivatives [16]. For example, Mo(CO)6-TMNO-promoted cyclization of the optically active alkynyl alcohol 42, prepared utilizing Sharpless asymmetric epoxidation, afforded dihydrofuran 43 in good yield. Iodine-mediated introduction of a thymine moiety followed by dehydroiodination and hydrolysis of the pivaloate gave stavudine in only six steps starting from allyl alcohol (Scheme 5.13). 

Asymmetric addition to aldehydes. In the presence of 1, lithium trimethylsilyl-acctylide reacts with aliphatic aldehydes to form predominately (R)-alkynyl alcohols. One of these products was converted into optically active 5-octyl-2(5//)-luranonc (2) as shown in equation (I).1... 

The rhodium-catalysed addition of alkynes to 1,2-diketones, 1,2-keto esters, and aldehydes has provided a method for the synthesis of tertiary alkynyl alcohols under... 

Alkynyl alcohols, silylative lactonization, 11, 493 Alkynyl aldehydes, in [5+2+l]-cycloadditions, 10, 632 Alkynyl alkali metal derivatives, characteristics, 2, 17 Alkynyl amides, in [5+2+l]-cycloadditions, 10, 632... 

A tungsten-catalyzed cycloisomerization of the D-ribose-derived alkynyl alcohol 181 provides a 6-endo-dig cyclization route to 3,4-dihydropyrans. Excellent endo-modc selectivity, and hence minimal tetrahydrofuran production is... 

Because unsaturated lactones and lactams are of importance as biologically active compounds, the carbonylative cyclization of alkynyl alcohols, alkynyl amines, and their allenyl derivatives has been extensively studied using various transition-metal complexes. Takahashi et al. [35] reported that Ru3(CO)12 also catalyzes the cyclocarbonylation of allenyl alcohols to five- to eight-membered unsaturated lactones (Eq. 20). 

In addition, a recent discovery that potassium 3-aminopropyl amide (KAPA)771 isomerizes internal alkynyl alcohols to the terminal alkynes without racemization,78)... 

The trans allylic alcohol needed to make this compound was made using one of the methods we introduced in Chapter 3i reduction of an alkynyl alcohol with LiAlEL]. Here is the full synthesis alkylation of an ester enolate with prenyl bromide gives a new ester, which itself is turned into an alkylating agent by reduction and tosylation. The alkyne is introduced as its lithium derivative with the alcohol protected as a THP acetal. Hydrolysis of the acetal with aqueous acid gives the hydroxy-alkyne needed for reduction to the E double bond, which is then epoxidized. 

In contrast, morpholine enamines from higher alkyl ketones do not dimerise but undergo disproportionation to the reduced enamine and various oxidation products. Aldehyde enamines dimerise, but with more difficulty at higher temperatures544. Cross-conjugated545 and linear dienamines (e.g. 132)546 have been prepared by condensation of amide acetals with alkynyl alcohols (equation 37). 

A one-pot synthesis of benzolactones and lactams via a cobalt-catalyzed regioselective [2-f2-f2] co-cyclotrimeriza-tion of alkynyl alcohols and amines with methyl propiolate has been described (Equation 54) <2005CC4955>. 

Enantloselective ethynylation of benzaldehyde, The reaction of benzaldehyde with lithium trimethylsilylacetylide in the presence of 1 in DME affords the corresponding (S)-alkynyl alcohol 2 in 92% optical yield. The optical yield is —75% with lithium acetylide itself. 

The optically active alkynyl alcohols are converted into the corresponding optically active 4-alkyl-7-butyrolactones and 4-alkylbutenolides. ... 

Enantioselective Addition of Various Organozinc Reagents to Aldehydes. Catalytic enantioselective addition of dialkynylz-inc reagents to aldehydes using (1 S,2R)-DBNE (20 mol %) affords optically active (R)-alkynyl alcohols with 43% ee in 99% yield. When an alkylalkynylzinc is used with (lS,2/ )-DBNE (5 mol %), an alkynyl alcohol with 40% ee is obtained. When 2-phenylzinc bromide is reacted with an aldehyde in the presence of 1 equiv of the lithium salt of (li ,25)-(l), the corresponding alkynyl alcohol is obtained in 88% ee (eq 8). ... 

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