Alkynolates

The reaction of perfluoroalkyl iodides with alkenes affords the perfluoro-alkylated alkyl iodides 931. Q.a-Difluoro-functionalized phosphonates are prepared by the addition of the iododifluoromethylphosphonate (932) at room temperature[778], A one-electron transfer-initiated radical mechanism has been proposed for the addition reaction. Addition to alkynes affords 1-perfluoro-alkyl-2-iodoalkenes (933)[779-781]. The fluorine-containing oxirane 934 is obtained by the reaction of allyl aicohol[782]. Under a CO atmosphere, the carbocarbonylation of the alkenol 935 and the alkynol 937 takes place with perfluoroalkyl iodides to give the fluorine-containing lactones 936 and 938[783]. 

Addition of a hydroxy group to alkynes to form enol ethers is possible with Pd(II). Enol ether formation and its hydrolysis mean the hydration of alkynes to ketones. The 5-hydroxyalkyne 249 was converted into the cyclic enol ether 250[124], Stereoselective enol ether formation was applied to the synthesis of prostacyclin[131]. Treatment of the 4-alkynol 251 with a stoichiometric amount of PdCl2, followed by hydrogenolysis with formic acid, gives the cyclic enol ether 253. Alkoxypalladation to give 252 is trans addition, because the Z E ratio of the alkene 253 was 33 1. 

In 1991, El-Ali and Alper reported the cyclocarbonylation reaction of terminal propargyl alcohols with formation of 5,5-disubstituted 2(5//)-furanones using Pd(dba)2 and l,4-bis(diphenylphosphino)butane (dppb) (91JOC4099). However, this reaction was not applicable to internal alkynols. 

Recently, a modified procedure for this reaction was reported, extending its utility to internal alkynols with alkyl, phenyl, and vinyl units (R = H, alkyl, Ph,... 

The palladium-catalyzed reaction of o-iodoanilides with terminal acetylenic carbinols provides a facile route to the synthesis of quinolines using readily available starting materials (93TL1625). When o-iodoanilide 126 was stirred with acetylenic carbinol 127 in the presence of bis-triphenyl phosphine palladium(ll) chloride in triethylamine at room temperature for 24 h, the substituted alkynol 128 was obtained in 65% yield. On cyclization of 128 with sodium ethoxide in ethanol, 2-substituted quinoline 129 was obtained in excellent yield. 

Scheme 8.34 Polyol systems by cross-coupling of six-carbon alkynol modules.

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. 

Bis(trimethylsilyl)propyne, 141 Bis(trimethylsilyl)terminai alkynols, 97 Borane-dimethyl sulphide. 84 Bromination-dcsilicobromination, 17-18... 

Reaction of alkynols 156 with benzenesulphenyl chloride afforded either the vinylacety-lene sulphoxides 157 or the allene sulphoxides 158 depending upon the substitution pattern of alkynols 156. Vinylacetylene sulphoxides 157 result from a [2,3]-allylic rearrangement of the sulphenate ester 159 (equation 88). In the case of the cyclic... 

Rearrangement of acetylenic sulphenates to the allenic sulphoxides 151 was discovered when the synthesis of propargylic ester of trichloromethanesulphenic acid 152 was attempted (equation 86). This reaction is of general scope and gives very good yields of allenic sulphoxides (Table 14) from structurally diverse cohols and various sulphenyl chlorides Reaction of alkynols 153 with benzenesulphenyl chloride in the presence... 

Recently, a Pd/Cu-catalyzed three-component coupling reaction of aryl halides, norbomadiene, and alkynols was reported to generate 2,3-disubstituted norbomenes in high yields in the presence of aqueous NaOH and a phase-transfer catalyst in toluene at 100°C (Eq. 3.39).151... 

VII. Reactions of OsHCl(CO)(PiPr3)2 with Alkynols Formation of... 

REACTIONS OF OsHCI(CO)(P Pr3)2 WITH ALKYNOLS FORMATION OF a,p-UNSATURATED CARBENE COMPLEXES... 

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). 

The formation of the complexes shown in Scheme 14 and Eq. (5) has been rationalized according to Scheme 15. Thus, it has been proposed that the insertion of the Os—H bond of OsHCl(CO)(P Pr3)2 into the carbon-carbon triple bond of the alkynol initially gives five-coordinate (E )-alkenyl intermediates, which subsequently isomerize into the Os CH=CHC(OH)R1R2 derivatives. The key to this isomerization is probably the fact that the five-coordinated ( )-alkenyl intermediates are 16-electron species, while the Os CH=CHC(OH)R1R2 derivatives are... 

Reaction of a phosphorus halide with a 2-alkynol and subsequent rearrangement to generate a hydroxyphosphonate... 

Another possible termination step that has been utilized for the cycloetherification of alkynols involves CO insertion and esterification of the resulting acyl metal with an exogenous alcohol. This process has typically employed MeOH as solvent and a stoichiometric oxidant since the catalyst is turned over in a reduced form. Following this mechanistic motif, a variety of alkynols have been cyclized under Pd(n) catalysis to five- and six-membered oxacycles with incorporation of methyl esters into the products.294,327-329 For the formation of five-membered ring products, this reaction has been carried out in both exo- and endo-mode to provide 1- and 2-substituted... 

In addition to the W and Mo carbonyl complexes that have most commonly been used for the cycloisomerization of alkynols, an Rh-based catalyst system has recently been developed which uses substantially lower catalyst loadings (1.5-2.5 mol%) than have typically been required for the W and Mo systems (10-50 mol%).369 Among the various ligands studied, P(/>-F-C6H4)3 proved to be particularly effective. Interestingly, this ligand has also been found to be optimal for an Ru system that catalyzes the same type of cycloisomerization (Equation (104)).370,371... 

Substituting the benzene ring with a double bond, Pd-catalyzed intramolecular alkoxylation of alkyne 122 also proceeded via an alkenyl palladium complex to form furan 123 instead of a benzofurans [99, 100]. In addition, 3-hydroxyalkylbenzo[fc]furans was prepared by Bishop et al via a Pd-catalyzed heteroannulation of silyl-protected alkynols with 2-iodophenol in a fashion akin to the Larock indole synthesis, [101]. 

Figure 7. Crystal structure of alkynol 11 in the (100) layer. C-H—O and C-H—jt hydrogen bonds are indicated. The hydrocarbon and hydrogen bonded regions both lie in the plane of the drawing signifying heavy structural interference between these domains.

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