Esters hydroxy propargylic

Rh complexes are examples of the most effective catalysts for the polymerization of monosubstituted acetylenes, whose mechanism is proposed as insertion type. Since Rh catalysts and their active species for polymerization have tolerance toward polar functional groups, they can widely be applied to the polymerization of both non-polar and polar monomers such as phenylacetylenes, propiolic acid esters, A-propargyl amides, and other acetylenic compounds involving amino, hydroxy, azo, radical groups (see Table 3). It should be noted that, in the case of phenylacetylene as monomer, Rh catalysts generally achieve quantitative yield of the polymer and almost perfect stereoregularity of the polymer main chain (m-transoidal). Some of Rh catalysts can achieve living polymerization of certain acetylenic monomers. The only one defect of Rh catalysts is that they are usually inapplicable to the polymerization of disubstituted acetylenes. Only one exception has been reported which is described below. 

AUenes are proposed as intermediates in the gold(I)-catalyzed cycloisomerization of P-hydroxy propargylic esters to afford dihydro-2H-pyrans l/2f/-pyrans 2 (Scheme 1) (13T8002). 

Cycloisomerization of )9-hydroxy propargylic esters to dihydropyrans/2//-pyrans, via 1,3-carboxylate migration followed by regioselective hydroxyl addition to a transient allene intermediate, has been catalysed by PhjPAuCl/AgSbFg (Scheme 126). ... 

The above two consecutive transformations provide straightforward access from propargyl alcohols to cyclopropene derivatives with an a- or /1-hydroxy group. This simple method is complementary to the access to 3-hydroxymethylcyclopropenes, via Rh2(OAc)4 catalyzed addition of diazoacetate to alkynes followed by reduction of the ester group, a route that is restricted to the access of primary cyclopropenyl alcohols [57], and is an alternative to the use of 2,2-dibromo-l-chlorocyclopropane via cyclopropenyl Uthium. 

Not least for the syntheses of natural products, alkoxycarbonylations with formation of allenic esters, often starting from mesylates or carbonates of type 89, are of great importance [35, 137]. In the case of carbonates, the formation of the products 96 occurs by decarboxylation of 94 to give the intermediates 95 (Scheme 7.14). The mesylates 97 are preferred to the analogous carbonates for the alkoxycarbonylation of optically active propargylic compounds in order to decrease the loss of optical purity in the products 98 [15]. In addition to the simple propargylic compounds of type 89, cyclic carbonates or epoxides such as 99 can also be used [138]. The obtained products 100 contain an additional hydroxy function. 

Whereas the Markovnikov addition of carboxylic acids to propargylic alcohols produces P-ketoesters, resulting from intramolecular transesterification [30, 31], the addition to propargylic alcohols in the presence of Ru(methallyl)2(dppe) 1 at 65 °C leads to hydroxylated alk-l-en-l-yl esters via formation of a hydroxy vinylidene intermediate [32, 33]. The stereoselectivities are lo ver than those obtained from non-hydroxylated substrates. These esters, which are protected forms of aldehydes, can easily be cleaved under thermal or acidic conditions to give conjugated enals, corresponding to the formal isomerization products of the starting alcohols (Scheme 10.6). 

Propargylic alcohols are also very interesting because anti-Markovnikov addition of benzoic acid generates bifunctional 1,3-hydroxy esters with addition of the car-boxylate to the terminal carbon of the triple bond [14, 15]. This reaction contrasts... 

The addition to propargylic alcohols in the presence of Ru(methallyl)2-(dppe) (B) at 65 °C leads to hydroxylated alk-l-en-l-yl esters via formation of a hydroxy vinylidene intermediate [27,28]. These esters can easily be cleaved... 

The coupling reaction of a-keto esters with allyl, propargyl, and allenyl halides using indium metal in aqueous solvents affords a-hydroxy-y,<5-unsaturated esters (Equation (28)).197,198 1,3-Dicarbonyl compounds undergo efficient carbonyl allylation reactions in an aqueous medium through a Barbier-type reaction (Equation (29)). The reaction is general and a variety of 1,3-dicarbonyls has been alkylated using allyl bromide or allyl chloride in conjunction with indium.199... 

In the presence of RuCl2(PPh3)(arene) or [Ru(02CH)(CO)2(PPh3)]2, propargylic alcohols do not afford hydroxy enol esters but /3-ketoesters according to Scheme 8.15... 

Heterocyclization. The alkoxycarbonylation of propargylic tunines and (Z)-enynes containing an allylic hydroxy group is participated by the heteroatom(s), forming oxazolidinones and 2-furylacetic esters, respectively. 

The reductive carbonylation of propargyl alcohols in the presence of thiols which results in P,y-unsaturated thioesters is in contrast to the formation of 5-hydroxy-2,3-alkadienoic esters from ethynyloxiranes. 

Scheme 47). In the synthesis of 9-acetoxyfukinanolide (140), the propargyl ester derived from the precursor 138 underwent successful cyclization to yield the lactone 139 [95] (Scheme 48). A retroaldol-aldol sequence on the hydroxy lactone derivative resulted in the epimerization at the quaternary diastereogenic center leading to the natural configuration. The allylic propiolate 141 reacted with tribu-tylstannane to produce the Z-a-stannylmethylene-y-butyrolactone 142, which served as an intermediate in the stereoselective synthesis of gadain (143) [96] (Scheme 49). 

Resolution by transesterification. Using vinylic acetates to esterify allyl alcohols, propargyl alcohols, 2-phenylthiocycloalkanols, a-hydroxy esters," methyl 5-hydroxy-2-hexenoates, and 2-substituted 1,3-propanediols, the enantioselective esterification provides a means of separation of optical isomers. Vinyl carbonates are also resolved by lipase-mediated enantioselective conversion to benzyl carbonates. Other esters that have also been used in the kinetic resolution include 2,2,2-tri-fluoroethyl propionate. There is a report on a double enantioselective transesterification" of racemic trifluoroethyl esters and cyclic meso-diols by lipase catalysis. 

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