Alkynol compounds

Structural diversity in gew-alkynol compounds, which have hydroxyl and ethynyl groups juxtaposed on the same carbon atom, is now discussed. Both functional groups can behave as hydrogen bond donors (O-H and C=C-H) and acceptors (O-H and... 

Using sulphonic acid ion-exchange resins in ether solvent, selective removal of the trimethylsilyl group from oxygen in bistrimethylsilylated terminal alkynols can be achieved. This method is particularly suitable for low-molecular-weight compounds, where water solubility would make efficient extraction from an aqueous layer difficult. 

The reactivity of OsHCl(CO)(P Pr3)2 toward alkynols depends on the substituents at the C(OH) carbon atom of the alkynol (Scheme 14).47 The reaction with 2-propyn-1 -ol initially affords the alkenyl compound 6s(CI I=CI ICII2OI I)Cl(CO) (P Pr3)2 in 85% yield, as a result of the anti-addition of the Os—H bond to the carbon-carbon triple bond of the alkynol. In chloroform-df solution this complex decomposes to a mixture of products, containing the derivatives OsCl2(CHCH=CH2) (CO)(P Pr3)2 and 6s(CHCHCH6)Cl(CO)(P Pr3)2 (Eq. 5). 

Alumina, in alkynol hydration-dehydration reactions, 6, 841 Aluminate organic liquids, characteristics, 1, 852 Alumination, direct, aromatic rings, 9, 267 Aluminum(III) alkyl compounds... 

Conversion of alkynols into iodo-unsaturated carbonyl compounds using HTI and... 

To a solution of 10 mmol of alkynol in 5 mL of Et20 are added 10 mmol of a base. At 0 "C, 10 mmol of a chlorophosphine are added under an inert atmosphere. The reaction mixture is kept at r.t. for 24 h (Method A), or heated at 80 C for 45 min (Method B), then hydrolyzed and extracted with Et,0 The ethereal layer is washed twice with 3-mL portions of diluted NH3 and H20. Crude compounds are crystallized from hexane, pentane or cyclohexane. 

Besides the conventional methods, the metallo-carbene route to access cyclic compounds has become a versatile tool in sugar chemistry. Synthesis of stavudine 112, an antiviral nucleoside, from an allyl alcohol [101] is realized by a Mo(CO)5-mediated cyclization reaction (O Scheme 26). Molybdenum hexacarbonyl smoothly reacts with the triple bond of 113 to generate the intermediate Mo-carbene, which undergoes a clean cyclorearrangement to yield the furanoid glycal 114. Alkynol isomerization is effected by group-6 transition metal carbonyl complexes [102]. 

The lower reactivity of iridium complexes requires the use of more activated precursors. Thus, the neutral square-planar derivatives Zra .v- IrCI =C=C=C(R)Ph (Pz -Prs)2] (R = Ph, f-Bu) have been prepared from [IrH2Cl(Pz-Pr3)2] and the appropriate alkynol, via UV-promoted or CF3CO2H-catalyzed dehydration of the initially formed hydride-alkynyl intermediates [IrHCl C=CC(R)Ph(OH) (Pz-Pr3)2] [78, 81]. The cationic species [Ir(=C=C=CPh2)(/ -diene)( PR3) [BF4] (diene = COD, PR3 = PCys diene - TFB, PR3 - PCys, P/-Prs) are also known [211], They were synthesized by reacting the methoxo compounds [Ir(OMe)(z/ -diene)(PRs) with l,l-diphenyl-2-propyn-l-ol, followed by dehydration of the resulting alkynyl derivatives [Ir C=CCPh2(OH) (77 -diene)(PRs)] with stoichiometric amounts of HBF4. 

Three important processes have evolved from Reppe s work. Vinylation, the formation of vinyl derivatives by reaction of such compounds as acids, glycols, and alcohols with acetylene, produces the important vinyl esters and vinyl ethers. Ethinylation is defined as the reaction of acetylene with the carbon atom of a reactant without loss of the triple bond. A major application of the ethinylation reaction is to aldehydes and ketones to give alkynols and alkyndiols—e.g., the reaction of acetylene with formaldehyde to give propargyl alcohol and butyn-2-diol-l,4. Carboxylation (also referred to as carbonylation), the reaction of acetylene with carbon monoxide in the presence of metal carbonyls, has been applied to the production of acrylic acid, acrylates, and hydroquinone. 

Jackson, W.R., Lovel, C.G., Perlmutter, P., and SmaUridge, A. 1988. The stereochemistry of organometallic compounds. XXXI. Hydrocyanation of alkynols. Australian Journal of Chemistry, 41 1099-1106. 

In agreement with the tendency shown by 133 to release a phosphine ligand, the treatment of this compound with 1 equiv of l,l-diphenyl-2-propyn-l-ol in pentane at room temperature leads to the 71-alkynol complex Os(ti5-C5H5)C1 ti2-HCsC(OH)Ph2 (P Pr3) (150). In toluene at room temperature, this compound is stable. However, at 85 °C, it evolves into the allenylidene derivative Os(ti5-C5H5)Cl(C=C=CPh2)(P Pr3) (151), which has a very remarkable nucleophilic character [58]. 

Although reaction intermediates have not been isolated, it has been proposed that the catalytic addition of c u-boxylic acids to prop-2-yn-l-ols, in the presence of transition-metal compounds, requires the initial -coordination of the alkynol to the metallic center, with subsequent attack of the carboxylato group at the coordinated carbon-carbon triple bond of the alkyne [61]. The reactions shown in Scheme 41 are strong evidence in favour of this proposal by isolating complexes which are examples of species proposed as intermediates in these catalytic transformations. 

The most general approach to the preparation of functionalized acetylenes including acetylenic ethers involves elimination techniques, mostly dehydrohalogenation of appropriate olefin precursors (see Sections II.D.l and III.A.l). However, these and related procedures do not work for the preparation of alkynol esters 94-96, and this undoubtedly is one of the major reasons why these compounds remained unknown until the mid-1980s4 5. 

Reduction of the lactone 137 to the corresponding lactol 138 necessitated use of DIBAL quenching the reaction with methanol followed by workup with aqueous potassium sodium tartarate furnished the product as a clear viscous oil that solidified on standing to a white solid. The anomeric hydroxyl group was conveniently protected by the formation of terf-butyldimethylsilyl ether by treatment with rert-butyldimeth-ylsilyl chloride, imidazole, and A,A-dimethylaminopyridine. Further activation of the anomeric position in compound 139 with trimethylsilyl bronfide followed by treatment with l-t-butyldimethysiloxy-3-butyne and n-butyUithium yielded a transicis mixture (1 1) (140) that was used without further purification. Reaction of compound 140 with tetrabutylammonium fluoride led to deprotection of the hydroxy functionality. The resulting transicis mixture of the alkynols was subjected to extensive chromatography and repeated crystallization to obtain a tran -alcohol (141) as a white crystalline solid. Further elaboration to 131 was carried out by appropriate modifications of a literature procedure. ... 

The asymmetric synthesis of compound 43, a precursor for the preparation of 2, 3 -didehydro-2, 3 -dideoxy thymidine and cordecepin, has been accomplished by reacting the chiral alkynol 44 with the reagent combination molydenum pentacarbonyl-triethylamine. Several other glycals were prepared in a similar way, with the formation of furan by-products sometimes observed. ... 

F-Alkenyltin compounds may be prepared by transmetallation using triorganyltin halides. Several ( )-alkenylstannyl alcohols have been prepared from intramolecular cross-coupling in the synthesis of zearalenone shown in Scheme 12. ... 

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