Alkynes hydroxy

Isomerization of a-hydroxy alkynes and alkynones 2-15 Acylation of olefins 2-27 From lithium acetylides 2-32 From vinylic organometallic compounds... 

The reaction is highly dependent on the alkyne used. When structurally simple 3-hydroxy alkynes such as propargyl alcohol are used, acceptable yields of the addition products are obtained, whereas reactions with alkynes prone to carbocation formation and rearrangement, such as 1-ethynyl-cyclohexanol, give a complex mixture of products.68,73... 

The trans allylic alcohol needed to make this compound was made using one of the methods we introduced in Chapter 3i reduction of an alkynyl alcohol with LiAlEL]. Here is the full synthesis alkylation of an ester enolate with prenyl bromide gives a new ester, which itself is turned into an alkylating agent by reduction and tosylation. The alkyne is introduced as its lithium derivative with the alcohol protected as a THP acetal. Hydrolysis of the acetal with aqueous acid gives the hydroxy-alkyne needed for reduction to the E double bond, which is then epoxidized. 

BuLi and AC2O of nitrooxaheptynes 20, generated in high yields from nitroalkenes and hydroxy alkynes <03H(59)685>. 

FVP experiments were carried out between 500 and 800 °G on 3(5)-phenyl- and 3(5)-methylpyrazolinones and on 3(5)-methoxy-5(3)-phenylpyrazole < 1999J(P2)211 >. The origin of the isolated products (mainly indanone, hydroxy-alkynes, and a,/ -unsaturated aldehydes) were explained as arising from the hydroxy tautomers of pyrazolinones. Temperature effects on the tautomeric equilibrium of 1-phenyl-3-methylpyrazolinone in solution show that the percentage of the GFI tautomer increased with increasing temperature. 

With a more complicated substrate 48, Suzuki et al. [34] removed the benzyl protecting group by use of calcium in ammonia, in which part of the diol product underwent partial saturation of the triple bond (Scheme 4.13). Hydrogenation of this mixture gave the fully saturated diol 49 in 87% yield. A thorough study was performed on selective reduction of benzyloxy alkyne 50 to give a mixture of hydroxy alkyne 51 and hydroxy trans-alkene 52 in 81-93% overall yields (Scheme 4.14) [12]. The study involved the use of different quantities of calcium and lithium in liquid ammonia. 

Electrocatalytic additions of perfluoroalkyl iodides to 3-hydroxy-alkynes have been performed in aqueous KCl emulsions using a carbon fiber cathode. Radical chain mechanisms are responsible for... 

In 2007, Zhou and coworkers demonstrated that furo[3,2-c]coumarins can be alternatively assembled by coupling readily accessible 4-hydroxycoumarins with propargylic alcohols. Thus, as shown in Scheme 8, they were able to synthesize the multisubstituted furo[3,2-c]coumarin 21 from 4-hydroxycoumarin and 1,3-diphe-nyl-2-propyn-l-ol through a two-step process involving the initial propargylation of the coumarin, by means of catalytic Yb(OTf)3, and a subsequent base-promoted cycloisomerization of the resulting hydroxy-alkyne 20 [66]. Related two-step transformations were later described employing catalytic tris(pentafluorophenyl)borane instead of Yb(OTf)3 [67]. 

The ketones resulting from the hydration of alkynes are useful chemical intermediates. For these reasons, attempts to develop nonmercury alkyne hydration were pursued. The system Nafion(Pd ) resin catalyst was the first reported to be active for the hydration of alkynes, including a-hydroxy alkynes, giving in high selectivity a-hydroxy-ketones [78]. At the same time, Cacchi and coworkers described the Pd(ll)-catalyzed hydration of enynes as key-step involved in a sequential process starting from vinyl triflates and affording y-hydroxy-a, p-enones [79]. 

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