Alkynes reactions with alcohols

Alkynylbenzaldehydes yield isochromenes in a Pd-catalysed reaction with alcohols. The Pd plays a dual role, behaving as a Lewis acid to effect the formation of a hemiacetal and coordinating to the alkyne moiety to promote cyclic ether formation <02JA764>. 

The U—C bond length in the metallacyclic unit is unusually long (2.752(11) A), and is susceptible to protonation by alcohols, amines, and terminal alkynes reaction with pyridine leads to the generation of a r/ -pyridyl complex. 

Isomerizations. A convenient method for the conversion of alkynes to conjugated dienes is by treatment with Ph P. The synthetic application is shown in the preparation of 2,4-alkadienols from 2-alkynoic acids involving esterification with pentafluorophenol, isomerization with PhjP (PhMe, 50°), and reduction with DIBAL-H. Even propargyl bromide can be isomerized to give 1-bromopropadiene, albeit in 29% yield. Conjugated alkadienoic esters and amides are obtained in one step from the pentafluorophenyl alkynoates on reaction with alcohols and amines, respectively, after treatment with catalytic amount of PhjP. 

CHLORCYAN (506-77-4) CNCl C-N-CL Noncombustible gas. Violent polymerization can be caused by chlorine or moisture. Violent reaction with alcohols, alkenes, and alkynes (violent exothermic reaction) acids, acid salts, amines, strong alkalis, olefins, strong oxidizers. Contact with acid forms toxic hydrogen cyanide gas. Mixtures with benzene or cyanogen halides yield hydrogen chloride. In cmde form, this chemical trimerizes violently if catalyzed by traces of hydrogen chloride or ammonium chloride, forming cyanuric chloride. Alkaline conditions will convert this chemical to... 

Substitution reactions. Replacement of the hydroxyl group of l-alkyn-3-ols on reaction with alcohols, thiols, and amines is accomplished at room temperature in the presence of binuclear complex 1 and NH4BF4. 

Addition reactions of alcohols to alkenes and alkynes have already been provided (Chapter 6) and a few more are shown in Table 8.6. Further, although many more addition reactions will be encountered later in the text (when the functional group with which the alcohol, enol, or phenol reacts is discussed in more detail), an introduction to some of the more common reactions is provided in Table 8.6. The table presents some of the partners of addition reactions with alcohols, enols, and phenols and the products they form together. The reactions shown are typical and, as such, are briefly discussed. 

A number of processes catalyzed by the dithiolate-bridged species have been mentioned already however, the extensive reactivity of alkynes within these systems has led to a number of more recent reports on their use in catalysis. The allenylidene complex 363 (R = Tol, R = Me 864 salt) has been identified as an intermediate in the catalysis of propargylic alcohol substitution reactions with alcohols in high yields and with complete regioselectivities... 

CO. Alkynes will react with carbon monoxide in the presence of a metal carbonyl (e.g. Ni(CO)4) and water to give prop>enoic acids (R-CH = CH-C02H), with alcohols (R OH) to give propenoic esters, RCH CHC02R and with amines (R NH2) to give propenoic amides RCHrCHCONHR. Using alternative catalysts, e.g. Fe(CO)5, alkynes and carbon monoxide will produce cyclopentadienones or hydroquinols. A commercially important variation of this reaction is hydroformyiation (the 0x0 reaction ). 

Propargylic alcohol, after lithiation, reacts with CO2 to generate the lithium carbonate 243, which undergoes oxypalladation. The reaction of allyl chloride yields the cyclic carbonate 244 and PdC. By this reaction hydroxy and allyl groups are introduced into the triple bond to give the o-allyl ketone 245[129]. Also the formation of 248 from the keto alkyne 246 with CO2 via in situ formation of the carbonate 247 is catalyzed by Pd(0)[130]. 

Examples of the protection of alkynes, carboxylic acids, alcohols, phenols, aldehydes, amides, amines, esters, ketones, and alkenes are also indexed on p. xvii. Section (designated with an A 15A, 30A, etc.) with protecting group reactions are located at the end of pertinent chapters. 

Unlike the case of the Ni-catalyzed reaction, which afforded the branched thioester (Eq. 7.1), the PdCl2(PPh3)3/SnCl2-catalyzed reaction with 1-alkyne and 1-alkene predominantly provided terminal thioester 6 in up to 61% yield in preference to 7. In 1983, a similar hydrothiocarboxylation of an alkene was also documented by using a Pd(OAc)2/P( -Pr)3 catalyst system with t-BuSH to form 8 in up to 79% yield (Eq. 7.6) [16]. It was mentioned in the patent that the Pt-complex also possessed catalyhc activity for the transformation, although the yield of product was unsatisfactory. In 1984, the hydrothiocarboxylation of a 1,3-diene catalyzed by Co2(CO)g in pyridine was also reported in a patent [17]. In 1986, Alper et al. reported that a similar transformation to the one shown in Eq. (7.3) can be realized under much milder reaction conditions in the presence of a 1,3-diene [18], and the carboxylic ester 10 was produced using an aqueous alcohol as solvent (Eq. 7.7) [19]. 

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