Acetic 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) (-)... 

SYNS ACETIC ACID, ISOPROPENWE ESTER ISOPROPENAX ACETATE ISOPROPENYL ACETATE (DOT ISOPROPENYLESTER KYSELINY OCTOVE ... 

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... 

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). 

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. 

Acetylsucrose [63648-81-7] has been prepared in 40% yield by direct acetylation of sucrose using acetic anhydride in pyridine at 40° C (36). The 6-ester has subsequently been obtained in greater than 90% yield, by way of 4,6-cycHc orthoacetate. Other selective methods for the 6-acylated derivatives include the use of alkyl tin reagents such as dibutyl tin oxide (37) and of dibutyl stannolane derivatives (38). Selective acetylation of sucrose by an enzymic process has also been described. Treatment of sucrose with isopropenyl acetate in pyridine in the presence of Lipase P Amano gave, after chromatography, 6-0-acetylsucrose (33%) and 4/6-di-O-acetylsucrose (8%). The latter compound has been obtained in 47% yield by the prolonged treatment (39). 

Enol esters are another useful family of acylating agents. The acetate of the enol form of acetone, isopropenyl acetate, is the most commonly used member of this group of... 

A -Dien-3-ol esters e.g., acetates) have greater utility as reaction intermediates than as protecting groups. They are prepared from A" -3-ketones by reaction with the acetic anhydride"" or by exchange with isopropenyl acetate. 

Hence, enol esters such as isopropenyl acetate are good acylating agents for alcohols. Isopropenyl acetate can also be used to convert other ketones to the corresponding enol acetates in an exchange reaction ... 

Many such activated acyl derivatives have been developed, and the field has been reviewed [7-9]. The most commonly used irreversible acyl donors are various types of vinyl esters. During the acylation of the enzyme, vinyl alcohols are liberated, which rapidly tautomerize to non-nucleophilic carbonyl compounds (Scheme 4.5). The acyl-enzyme then reacts with the racemic nucleophile (e.g., an alcohol or amine). Many vinyl esters and isopropenyl acetate are commercially available, and others can be made from vinyl and isopropenyl acetate by Lewis acid- or palladium-catalyzed reactions with acids [10-12] or from transition metal-catalyzed additions to acetylenes [13-15]. If ethoxyacetylene is used in such reactions, R1 in the resulting acyl donor will be OEt (Scheme 4.5), and hence the end product from the acyl donor leaving group will be the innocuous ethyl acetate [16]. Other frequently used acylation agents that act as more or less irreversible acyl donors are the easily prepared 2,2,2-trifluoro- and 2,2,2-trichloro-ethyl esters [17-23]. Less frequently used are oxime esters and cyanomethyl ester [7]. S-ethyl thioesters such as the thiooctanoate has also been used, and here the ethanethiol formed is allowed to evaporate to displace the equilibrium [24, 25]. Some anhydrides can also serve as irreversible acyl donors. 

Below -ester products 85-92 via CALB-catalyzed acylation of rac-alcohols, isopropenyl acetate, room temp, until 50% conversion. Then Mitsunobu reaction ( DIAD, TPP, CH3COOH, ether 0 -> 20 °C, 24 h) ... 

In order to reduce the time needed to perform a complete kinetic resolution Lindner et al53 reported the use of the allylic alcohol 30 in enantiomerically enriched form rather than a racemic mixture in kinetic resolution. Thus, the kinetic resolution of 30 was performed starting from the enantiomerically enriched alcohol (R) or (S)-30 (45%) ee obtained by the ruthenium-catalyzed asymmetric reduction of 32 with the aim to reach 100 % ee in a consecutive approach. Several lipases were screened in resolving the enantiomerically enriched 30 either in the enantioselective transesterification of (<5)-30 (45% ee) using isopropenyl acetate as an acyl donor in toluene in non-aqueous medium or in the enantioselective hydrolysis of the corresponding acetate (R)-31, (45% ee) using a phosphate buffer (pH = 6) in aqueous medium. An E value of 300 was observed and the reaction was terminated after 3 h yielding (<5)-30 > 99% ee and the ester (R)-31 was recovered with 86% ee determined by capillary GC after 50 % conversion. 

A set of -methylene-/ -hydroxy esters 42 were resolved via enzymatic enantioselective transesterification with Pseudomonas sp. lipase (PCL), free and immobilized one using either vinyl or isopropenyl acetate as acyl donors under different conditions. The corresponding (R)-(+)-acetates (R)-43 and the unreacted (S)-(-)-substrates (S)-42 were obtained with an ee up to >99%.70... 

Various methods have been developed to shift the equilibrium between esterification and hydrolysis toward the ester formation.6 For example, as an acetyl donor, vinyl acetate and isopropenyl acetate have been used because the resulting unnecessary alcohol, vinyl or isopropenyl alcohol, spontaneously changes to the corresponding aldehyde or ketone as shown in Figure 6(c).6a... 

---