A- propargylic alcohols

Various nonracemic allenylstannanes have been prepared from nonracemic propargylic mesylates and (Bu3Sn)2CuLi. The stereochemistry of the displacement was shown to be anti by correlation with an allenic stannane prepared through Claisen orthoester rearrangement of a propargylic alcohol of known configuration (Scheme 33)80. 

Recently, reaction of a propargylic alcohol with diethyl chlorophos-phite in the presence of a tertiary amine has been found to be a facile method for the direct preparation of allenicphosphonates (Equation 4.37).167... 

An important variant for transition metal-catalyzed carbon-nitrogen bond formation is allylic substitution (for reviews, see1,la lh). Nucleophilic attack by an amine on an 7r-allyl intermediate, generated from either an allylic alcohol derivative,2 16,16a 16f an alkenyloxirane,17-19,19a-19d an alkenylaziridine19,19a 19d, or a propargyl alcohol derivative,21,21a 21d gives an allylic amine derivative. 

The use of a less reactive triethylgermyl derivative with a Pd(0)-phosphite catalyst achieves high yield germa-stannation of alkynes (Equation (127)).295 296 With this system, a propargylic alcohol as well as phenylacetylene is successfully transformed to the corresponding 1,2-adducts in good yield. 

This CrCl2/NiCl2-mediated coupling can also be used to obtain a propargylic alcohol with high diastereoselectivity (equation I). The aldehyde in this case under-... 

Other examples are based on the classical one-pot procedure starting from an orthoester, a catalytic amount of acid and a propargylic alcohol [553-558]. Estereno-lates react similarly [559, 560]. 

If the alkene is an alkyne instead, we are dealing with a propargylic alcohol and now the thermodynamics are more favourable and the product is an enone. Commercial application is found in the production of citral from dehydrolinalool via vanadium-catalysed isomerisation (Figure 5.9). Note that the last step involves a transfer of hydrogen as well when the enol rearranges to the aldehyde ... 

A preliminary experiment indicates the usefulness of similar complexation for Ritter reactions with a propargyl alcohol (equation II). 

The second step involves reduction of a propargylic alcohol to an F-allylic alcohol. 

Bagley et al. performed a number of pyrimidine and pyridine syntheses by condensing an inone—generated in situ by oxidation of a propargylic alcohol with IBX with amidines and p-aminocrotonate.108... 

A propargylic alcohol is selectively oxidized with active M11O2 in the presence of a primary aliphatic amine. The resulting alcohol condenses with the amine, thanks to the action of the added molecular sieves as dehydrating agent, leading to the formation of an imine in a very... 

Formation of Nucleophilic C21 via a Directed Reduction of a Propargyl Alcohol... 

In Section 6.3.6, it was emphasized that C02 and secondary amines could add to terminal alkynes in the presence of ruthenium catalysts to afford carbamates. Under comparable conditions (393-413 K, 5 MPa Ru-catalysts), primary amines will afford symmetrical disubstituted ureas in moderate yield [131]. It is worth noting that although the final urea does not contain the starting alkyne, its catalytic formation requires, besides the Ru-catalyst, the presence of a stoichiometric amount of a 1-alkyne (e.g., a propargylic alcohol). A possible mechanism (Scheme 6.32) for this catalytic reaction may involve activation of the alkyne at the metal center, a nucleophilic addition of the carbamate to the activated alkyne to produce... 

The terminal alkyne (or a propargylic alcohol, i.e. ethynyl carbinol)(l mmol) was added dropwise to a solution of BTI (516 mg, 1.2 mmol) in chloroform, or a mixture... 

Controlled reduction of alkynyl silanes produces the corresponding vinyl silanes and the method of reduction dictates the stereochemistry. Lindlar hydrogenation adds a molecule of hydrogen across the alkyne in a cis fashion to produce the 2-vinyl silane. Red Al reduction of a propargylic alcohol leads instead to the E-isomer. 

A related one-pot three component coupling reaction leading to allyli-dene tetrahydrofuran derivatives 80 and which combines a conjugate addition of a propargyl alcohol with an activated olefin and an in situ palladium-catalyzed carbopalladation-cyclization in the presence of a large excess of allyl chloride has been recently developed by Lu and Iiu (Scheme 31) [77]. The cyclization process is here initiated by addition of a catalytic amount of Pd(OAc)2 and in marked contrast with the above-discussed reactions, a catalytic cycle involving divalent palladium proceeds in the reaction. In this process, the ester enolate formed in the Michael addition undergoes... 

Apart from reactions where Michael addition terminated the process, Gabriele and co-workers have developed a useful and expedient palladium-catalyzed synthesis of 4-aminofuran-2-one 113 starting from three simple starting components, a propargyl alcohol, a dialkyl amine and carbon monoxide [98] (Scheme 44). 

A one-pot/two-reaction sequential ruthenium- and gold-catalyzed oxazole formation has been reported <2004CC2712>. The reaction of a propargylic alcohol and a primary amide in the presence of a Ru catalyst facilitates the formation of the intermediate propargyl amide which cyclizes upon treatment with AuCls (Scheme 61). 

Scheme 7-96 Hydrometallation of a propargylic alcohol followed by an allylzincation reaction.

Chemoselective semireduction of a propargylic alcohol triple bond in the presence of an isolated triple bond is feasible.- ... 

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