Propargyl Alcohols and Ethers

Ruthenium hydride complexes such as RuH(Cl)(PPh3)3(tol) (to = toluene) and RuH(Cl)(CO)(PPh3)3 can effect isomerization of propargyl alcohols and propargyl ethers to a,/l-unsaturated carbonyl compound and dienol ether, respectively [13]. 

Acetylenic silyl ethers are converted to the conjugated dienol silyl ethers by the catalysis of ruthenium hydride complexes (Eq. 12.8). 

In the reaction of dienol silyl ether derived from butyn-l,4-diol, conjugated dienol silyl ether 22 was obtained as a 1 1 mixture of (Z,Z) and (Z, ) stereo isomers. The 

In contrast to the reaction mode of the propargyl ethers, a,/3-unsaturated aldehydes and ketones are isolated in the catalytic isomerization of the propargyl alcohols. Trost et al. developed a new catalytic system, (IND)RuCl(PPh3)2/InCl3/ NH4PF13/THF (IND = -indenyl), that efficiently effected such isomerization [14]. The reaction is cocatalyzed by a mixture of NHEtBPFj and NH4PF6, and addition of indium trichloride accelerates the reaction (Eq. 12.9). 

The reaction exhibits extraordinary chemoselectivity and an isolated carbonyl group, ester, unprotected alcohol, alkyne and terminal alkene are unaffected by this catalytic system. Notably, the geometry of the resulting alkene moiety is controlled to be E (Eq. 12.10). 

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Most attention to date has been paid to the hydrostannation of propargyl alcohols and ethers where interaction of the Lewis-basic oxygen enhances the regio- and stereoselectivity and gives high yields of the Z-/3-adducts (e.g., Equations (20) and (21)), whereas hydrostannation with Bu3SnH gives only the Z-cr-adducts. 

In the case using Mo(CO)3(ButNC)3 as a catalyst, propargylic alcohols and ethers undergo highly regioselective a-hydrostannation regardless of their substitution pattern (Equation (33))."... 

Both l-bromo-3-methyl-l,2-butadiene (182) and 3-bromo-3-methyl-l-butyne (183) give in aqueous ethanol the same product mixture, containing mainly propargyl alcohol and ether, but no allenic derivative (Shiner and Humphrey, 1967). In the presence of both PhS and OH ions, an identical product mixture (32% allenic and 52% propargylic thioether) is again formed from both isomers. This and the rate acceleration by base were ascribed to the formation of a common allene-carbene intermediate which was written as (184a 184b) (Scheme 8). Since the... 

Scheme 10 6 Synthesis of conjugated trienes by carbomagnesiation of enyne propargylic alcohols and ethers [71],...

Treatment of alkenes such as 3-hexene, 3-octene, and 1-cyclohexyl-l-butene with the NHC-derived borane and catalytic HNTf2 (Tf=trifluoromethanesulfonyl, CF3SO2) affects hydroboration at room temperature. NHC-borenium cations (or functional equivalents) are postulated as the species that accomplish the hydroborations." Different NHC-CuCl complexes catalyse hydroborations of propargylic alcohols and ethers with opposite regioselectivity a 6-NHC-CuCl (23) complex provides a-selectivity, whereas / -selectivity is achieved using a 5-NHC-CuCl (24) complex." ... 

Regioselectivity of the CuCl-catalysed hydroboration of propargylic alcohols and ethers R C=CCH(OR )R with Pin2B2 can be controlled (from 98 2 to 2 98) by the steric bulk of the OR group and the NHC ligand to copper. A rationale has been provided by assuming different approach of the reactive species to the individual substrates (87)-(89).S9... 

The principal chemicals based on Reppe chemistry today are propargyl alcohol and butyn-l,4-diol and derivatives such as 2-pyrrohdinone, Ai-vinyl-2-pyrrohdinone, polyvinylpyrroHdinone, vinyl ethers, and tetrahydrofuran (33). 

R = Me, R = H) with cyclohexenol in the presence of F ion followed by NaOCl oxidation gave the tricyclic ether 61 in 65% yield (Scheme 9) [29]. The use of propargyl alcohol and propargyl thiol led, via the acetylenic oximes, to fused tetrahydrofuranoisoxazoles 62 a and 62 b, and tetrahydrothiopheno[3,4-c]isoxa-zole 62 c, respectively. Reaction of l-butyn-4-ol with 0-trimethylsilyl a-bro-moaldoxime 52e (R = R = Me) led to the tetrahydropyranoisoxazole 62 d. 

It was demonstrated that a variety of terminal alkynes, including propargylic alcohols or ethers, could also react with allylzinc bromide in THF. These reactions afforded mixtures of mono- and bis-addition products 295 and 296 respectively, presumably arising from... 

REPPE PROCESS. Any of several processes involving reaction of acetylene (1) with formaldehyde to produce 2-butync-l,4-diol which can be converted to butadiene (2) with formaldehyde under different conditions to produce propargyl alcohol and, form this, allyl alcohol (3) with hydrogen cyanide to yield acrylonitrile (4) with alcohols to give vinyl ethers (5) with amines or phenols to give vinyl derivatives (6) with carbon monoxide and alcohols to give esters of acrylic acid (7) by polymerization to produce cyclooctatetraene and (8) with phenols to make resins. The use of catalysis, pressures up to 30 atm, and special techniques to avoid or contain explosions are important factors in these processes. 

A mercury-free route to allyl vinyl ethers that relies on the Michael addition of allyl alcohols to unsubstituted alkenyl sulfoxides, followed by thermal loss of sulfenic acid and concurrent Claisen rearrangement has been described [145]. This methodology has been applied to the synthesis of isocar-bacyclin [146]. Posner reported an acid-catalyzed protocol that produces conjugated dienoate esters from allylic alcohols and a sulfinyl orthoester [147]. Additionally, the use of propargyl alcoholates and a chloro alkenyl sulfox-... 

The coupling of propargyl alcohol with copperfii) acetate in pyridine constitutes a notable exception to the kinetic behaviour described above , but it has been shown that the behaviour is peculiar to this particular system Thus normal kinetic behaviour is found for Cu(OAc)o-pyridine coupling of acetals and ethers of propargyl alcohol, and for propargyl alcohol itself when Cu(n) in aqueous ammonia is used . 

A similar approach had been reported earlier by Bestmann and coworkers" in their synthesis of hexadeuteriated leukotriene A4 methyl ester. C-alkylation of the tetrahy-dropyranyl ether of 3-butyn-l-ol with 2,2,3,3-tetradeuterio-l-iodopentane, prepared in 4 steps from propargyl alcohol, and subsequent protective group removal afforded the tetradeuteriated acetylenic alcohol 46 (equation 30). Semideuteriation of the alkynol and further transformation by known methods produced the labeled key reagent 3,4,6,6,7,7-hexadeuterio-(Z)-(3-nonen-l-yl)triphenylphosphonium iodide (47). Wittig olefination of epoxy dienal 45 with the labeled ylide generated from 47 completed the synthesis of... 

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. 

In a related approach bromomethyldimethylchlorosilane was used to silylate the hydroxyl group of propargyl alcohols and the resultant bromomethylsilyl ether reacted... 

In 2011,Jiang and co-workers showed a versatile alternative to the in situ preparation of the propargyl vinyl ethers starting from propargylic alcohols and acceptor-substituted alkynes (110BC7313).To this end, cyclic 1,3-diketones 25 and propargylic alcohols 24 were employed, and the corresponding enol ethers were obtained with iron(IIl) tosylate (Scheme 10)... 

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