Isopropenyl ester

Isopropenyl esters of N-protected amino acids. In the presence of the Ru(II) catalyst, Cbo- or Boc-amino acids add to propyne at 100° to provide isopropenyl esters in 55-85% yield with no racemization. Unprotected amino acids do not add to the alkyne. These esters react with primary amines at room temperature in ethyl acetate to afford amides in 75-90% yield. 

Isopropenyl acetate Acetic acid, isopropenyl ester (8) Acetic acid, (1-methylethenyl) ester (9) (-)... 

ACETIC ACID, IRON(2i-) SALT see FBHOOO ACETIC ACID, ISOBUTYL ESTER see IIJOOO ACETIC ACID, ISOPENTYL ESTER see IHO850 ACETIC ACID, ISOPROPENYL ESTER see MQK750 ACETIC ACID ISOPROPYL ESTER see INEIOO ACETIC ACID LEAD(2-i-) SALT see LCVOOO ACETIC ACID, LEAD(2-i-) S.ALT TRIHYDRATE see LCJOOO... 

Most of lipase-catalyzed acylations of sugars in organic solvents have been reported as transesterification rather than esterification reactions. The displacement of the equilibrium towards products has been accomplished by using activated acyl donors [58] such as 2,2,2-trichloroethyl esters and, more often, enol esters. The use of enol esters, such as a vinyl or an isopropenyl ester, was, in fact, first reported in lipase-catalyzed reactions with sugars [59]. In the reaction, an unstable enol is liberated which instantaneously tautomerizes to the corresponding aldehyde or ketone, making the reaction irreversible. 

A general route to acid fluorides, chlorides, bromides and iodides is provided by the reaction of enol esters, such as isopropenyl esters, with the appropriate hydrogen halide (equation 18). Phthalic acid dichloride in the presence of chlorosulfonic acid has been proposed as a reagent for the conversion of carboxylic esters to acid chlorides in high yield, as is shown in equation (19) for the cleavage of the ethyl ester of chlorofluoroacetic acid. °... 

Brief fusion of a mixture of isopropenyl esters and an acid catalyst with hydantoins gives high yields of N-acylated products.258 Treatment of hydantoins with trihalomethylsulfenyl chlorides yields N-3-substituted and N-l.N-3 disubstituted compounds, which exhibit antifungal activity.259 3-Aryl- or 3-alkylsulfonylhydantoins are prepared by direct acylation with RS02C1 in C5H5N or Et3N.260... 

The interaction of a alk-l-ene and phosphorus pentachloride to form a complex of the general composition RCH=CH2 2PCl5, now recognized as having the phosphonium salt structure 73, has been known for some time. Very many examples are now known of the decomposition of such complexes with SO2 (or in some cases with P40io ) under controlled conditions when the products are (2-chloroalkyl)phosphonic dichlorides (74) or derivatives thereof. The acids from but-l-ene and pent-l-ene hex-l-ene and hept-1-ene and oct-l-ene and dec-l-ene ° have all been reported. The stability of the initial adducts appears to very considerably, and dehydrochlorination may occur readily if the reaction is carried out with insufficient control. Vinyl and isopropenyl esters of carboxylic... 

The electrophilic activation of terminal alkynes by arene-ruthenium(II) catalysts has provided selective access to enol esters. Enol esters are much more reactive than alkyl esters and have been used in a variety of reactions. In the past decade, Dixneuf and co-workers have developed selective approaches to the Markovnikov and antz-Markovnikov addition of carboxylic acids across alkynes by employing different arene-ruthenium(II) catalysts [48,53,54]. Of special interest is the synthesis of AT-Boc-protected 1-alanine isopropenyl ester 110 from N-Boc-l-alanine 108 and propyne 109 mediated by (Ty -cymene)RuCl2(PPh3) complex 107 (Scheme 30) [53]. Addition of the amino acid 108 to the propyne 109 proceeded exclusively in the Markovnikov sense and without accompanying racemization of the substrate. 

Synonyms Acetic acid, isopropenyl ester 1-Acetoxy-1 -methylethylene 2-Acetoxypropene 2-Acetoxypropylene Methylvinyl acetate 1-Methylvinyl acetate 1-Propen-2-ol acetate 1-Propen-2-yl acetate Classification Carboxylic acid ester Empihcal C5H8O2 Formula CH3COOC(CH3) CH2 Properties Water-wh. liq. sol. in alcohol, ether, acetone mod. sol. in water m.w. 100.13 dens. 0.909 m.p. -93 C b.p. 97 C flash pt. (CC) 16 C ref. index 1.4020 (20 C)... 

Enol esters such as vinyl or isopropenyl esters liberate unstable enols as coproducts, which tautomerize to give the corresponding aldehydes or ketones [151,152] (Scheme 3.4). Thus, the reaction becomes completely irreversible and this ensures that all the benefits with regard to a rapid reaction rate and a high selectivity are accrued. Acyl transfer using enol esters has been shown to be about only ten times slower than hydrolysis (in aqueous solution) and about 10-100 times faster than acyl-transfer reactions using activated esters. In contrast, when nonactivated esters such as ethyl acetate were used, reaction rates of about lO -lO of that of the hydrolytic reaction are observed (Table 3.5) [153]. 

Currently, enol esters (1, ethoxjwinyl 5, vinyl and 6, isopropenyl esters Fig. 12) are the most useful irreversible acyl donors, because the liberated alcohol then is an enol that rapidly tautomerizes as shown in Figure 13. Economical vinyl acetate in particular is often favored, although acetaldehyde obtained can form an imine with free amino groups of the enzyme and lead to catalyst inhibition. In this sense, ethoxy vinyl esters, still rarely used acyl donors, are interesting, because they leave an alcohol that tautomerizes into harmless ethyl acetate (19). 

Synthesis.— The perennial interest in the esterification of carboxylic acids, particularly hindered ones, continues. Isopropenyl esters, prepared by the zinc(ii)-catalysed addition of the hindered acids to propyne, undergo ready acid-catalysed exchange with alcohols, as shown in Scheme 24,... 

Acylketenes l-(AIkoxy)enolethers a-Alkoxymethyleneketones Carboxylic acid isopropenyl esters Enolesters Enollactols Enollactones a, p-Ethyleneacetals a,0-Ethylenelactones a-Hydroxymethyleneketones 3-Keto-l, 2-en-l-olethers 3-Keto-l,2-en-l-ols a-Oxidoalcohols a,P-Oxidoketones Vinyl esters... 

A generally applicable method for the preparation of orthocarboxylic acid enol esters (32) is reported interchange of the corresponding triethyl orthoesters with /3-chloroalkanols and subsequent dehydrohalogenation gives the tris enol esters. Orthoformic acid tris isopropenyl ester, prepared in this manner, gives triacetoxymethane on ozonolysis. 

Isopropenyl esters, conveniently prepared from carboxylic acids and propyne in the presence of the zinc salt, readily effect the acylation of ise-thionic acid and of A-methyltaurine. ... 

The acetylation of amines with isopropenyl acetate appears to be a transition between the highly exothermic reactions of acyl halides and anhydrides with amines on the one hand and the reaction of amines with more conventional esters on the other. While this reagent is of particular value in the preparation of enol acetate, it has been used for the preparation of amides. One interesting aspect of its use is that acetone forms as a coproduct which may distill off as the reaction proceeds. Isopropenyl acetate and other isopropenyl esters may also be used to Y-acylate amides and imides. By the judicious selection of starting amides and isopropenyl esters, tertiary amides with three different acyl groups may be synthesized. This may very well be one of very few reaction systems which permits the synthesis of this rare group of tertiary amides. 

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