Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Crotonate esters

Other approaches to (36) make use of (37, R = CH ) and reaction with a tributylstannyl allene (60) or 3-siloxypentadiene (61). A chemicoen2ymatic synthesis for both thienamycia (2) and 1 -methyl analogues starts from the chiral monoester (38), derived by enzymatic hydrolysis of the dimethyl ester, and proceeding by way of the P-lactam (39, R = H or CH ) (62,63). (3)-Methyl-3-hydroxy-2-methylpropanoate [80657-57-4] (40), C H qO, has also been used as starting material for (36) (64), whereas 1,3-dipolar cycloaddition of a chiral nitrone with a crotonate ester affords the oxa2ohdine (41) which again can be converted to a suitable P-lactam precursor (65). [Pg.8]

Amine-containing cellulose esters, eg, the acetate A/A/-diethylaminoacetate (36) and propionate morpholinobutyrate (35), are of interest because of their unique solubiHty in dilute acid. Such esters are prepared by the addition of the appropriate amine to the cellulose acrylate crotonate esters or by replacement of the chlorine on cellulose acrylate chloroacetate esters with amines. This type of ester has been suggested for use in controlled release, mmen-protected feed supplements for mminants (36,37). [Pg.251]

The crotonate esters, prepared to protect a primary hydroxyl group in nucleosides, are cleaved by hydrazi ne (MeOH, Pyr, 2 h). The methoxycrotonate is 100-fold more reactive to hydrazinolysis and 2-fold less reactive to alkaline hydrolysis than the corresponding acetate. ... [Pg.100]

The above method is adapted from the procedure of Day and Thorpe.1 /3-Methylglutaric acid has been prepared by hydrolysis of jS-methylglutaronitrile 2 by condensation of crotonic ester with ethyl sodiocyanoacetate, and with sodiomalonic ester 3 4 and by condensation of acetaldehyde with malonic ester. ... [Pg.31]

In the hydroformylation of crotonate esters, three different aldehydes. may be formed, denoted as the a-, / -, or -y-isomers ... [Pg.35]

Crotonic esters and certain homologues, when converted to their enolates with LDA and treated with stannyl and germyl chlorides, afford the y-metallo derivatives (Table 10)57. In contrast, silylation of these enolates leads to the 0-silyl derivatives. Interestingly, the halostannane derivatives show a strong preference for the (Z) geometry suggestive of a donor-acceptor interaction between the carbonyl oxygen and the electropositive tin atom,... [Pg.227]

Alkylamino crotonic esters (22) all show in solution the presence of the isomers of both E and Z configurations, and there is also some evidence for rotamers involving restricted rotation about the (C=C)-N and C-C02R bonds (64). In all cases studied, when only one crystal form was found the molecular configuration was Z about the double bond. For R = CH2Ph, R = CJI, two crystal forms were obtained, one with E and one with Z molecular configuration. [Pg.149]

The double bond of certain a,p-unsaturated esters (e.g. crotonates, methacrylates) is so reactive that it tends to add the elements of the alcohol present as solvent the resulting p-alkoxy-substituted guanamines (LXXXV) (79) are therefore readily and cheaply produced, and the use of expensive p-alkoxycarboxylic esters required in the conventional synthesis (706) is avoided. Crotonic esters give the alkoxyguanamine... [Pg.47]

Syntheses of Self-Sensitized Polymers by Cationic Copolymerizations. The cationic polymerizations of several vinyl ethers containing pendant ester groups such as cinnamic ester 12), methacrylic ester 16), acrylic ester (77), and crotonic ester 18) have been reported. Based on these reports, cationic copolymerizations of CEVE with photosensitizer monomers such as NPVE, NNVE, VNP and NPEVE were carried out using TFB as a catalyst in toluene at — 65 °C. Each copolymer was obtained with high yield except in the case of copolymerization of CEVE with VNP as summarized in Table I. [Pg.228]

Amino-1,2,4-triazolo[l,5-a]pyrimidine derivatives (115) were prepared from 3,5-dihalo-l,2,4-triazoles (111) by amination followed by reaction with acrylic or crotonic ester (113) and then amination without the isolation of 112 and 114 [87T2497 88JAP(K)63/267782] (Scheme 22). [Pg.140]

Faraone, Parasacco, and Cogrossi (87) have introduced maleic and crotonic ester groups and methacryloyl ethylamine ether groups into partially acetylated celluloses. These cellulose derivatives containing substituents with polymerizable double bonds grafted with styrene when brought in contact in presence of benzoyl peroxide. [Pg.128]

Bestmann and Seng (5) reported that the reaction of methylene triphenylphosphorane with crotonic ester gave a cyclopropane derivative. We found that the less active carbomethoxymethylene triphenylphosphorane did not react with crotonic ester at all. [Pg.141]

When crotonate esters were employed the regioisomers 501 were mainly formed, accompanied by a significant amount of non-cyclic compounds 502 formally arising from insertion of the Si=C group in an ally lie C—H bond (equation 167). The reaction of silenes 149 and 150 with crotonate esters are the only examples known so far where the product distribution is different when the reaction is conducted under photolytic conditions or in the absence of light. Thus, in the dark reaction of 150 with methyl crotonate the relative ratio 501 (R1 = 1-Ad, R2 = Me) 502 (R1 = 1-Ad, R2 = Me) = 3.75 1 was obtained, while under photolytic conditions only minor amounts of 501 were detected245. The nominal insertion product 503 is also the major product in the reaction of methacrylate esters with 149 and 150 (equation 168). The minor product in this reaction is the l-sila-3-oxacyclohex-4-ene 504 (relative ratio 503 504 = 5.7 l)245. [Pg.965]

Note the analogy to the anions derived from crotonate esters. [Pg.33]

Vitamin A acid, especially used in the treatment of acne for some years, can also be obtained by Wittig reaction. Thus, olefination of phosphorane 506, with y-formyl-crotonic ester 509 as well as the reversed Wittig olefination, i.e. the conversion of aldehyde 511 and ylide 512 yields the ester 510 of vitamin A acid 255), according to Scheme 86. [Pg.146]

With fram-crotonic acid methyl ester, dimethylsulfoxonium methylide forms a cyclopropane stereoselectively (Figure 9.3, bottom). Therein, the methyl group and the COzMe group retain the trans orientation they had in the crotonic ester. Thus, the fnms-crotonic ester is cyclopropanated with complete retention of the configuration. [Pg.349]

It seems obvious that the same mechanism could also apply to the cyclopropanation of the fran,s-crotonic ester (Figure 9.3, bottom). A Michael addition of the S ylide would then convert it directly into the ester enolate B. This species would cyclize exclusively to the fratw-disubstituted cyclopropane exactly as when it is produced from the cis-crotonic ester in two steps via the conformer A. [Pg.350]

With crotonate esters, it was observed that the presence of the -methyl group spoiled the electrophilic reactivity an awfi-Michael selectivity prevailed over the. vyw-aldol selectivity (Scheme 34). The presence of three contiguous stereogenic centers in adduct 98 affords a mixture of four diastereomers (98A-98D), of which 98A and 98D were obtained as major isomers89. [Pg.84]

N-Substituted 3-aminocrotonic esters (67) tend to adopt a planar or near-planar structure. As a consequence of their push-pull nature these molecules show an increased facility for Z-67-is-67 isomerization around the C=C double bond as well as restricted rotation around the C—N and C—COOR2 single bonds. The IR and XH-NMR spectra of simple 3-(alkylamino)crotonic esters have shown that these substances exist either in the liquid state or in solution as equilibrium mixtures of the Z and E configurations, respectively. The position of the equilibrium is solvent-dependent, and the energy difference between the isomers varies from ca 7.3 kJ mol-1 in non-polar solvents to ca 0.8 kJ mol"1 in dimethyl sulphoxide, the intramolecularly bonded Z-form 68 or 69 being the most stable111-113. [Pg.240]

In agreement with frontier orbital considerations, crotonic esters add to nitrones to produce p-o o esters regioselectively. This reaction provides the basis for a synthesis of the Senecio alkaloid supinidine (7). Reaction of 1 with methyl 4-hydroxycrotonate yields the isoxazolidinone 5, which is easily converted to the... [Pg.507]

The same phosphonite also adds to crotonic esters (with... [Pg.136]

Similarly, the magnesium enolate of t-butyl (/ )-(p-tolylsulfmyl)acetate adds to aldehydes and ketones. The subsequent reductive desulfurization yields the corresponding optically active -hydroxy esters (Scheme 27). This process can be utiliz for preparation of a synthetic intermediate (95) of maytan-sine with a selectivity of 93 7 (equation 23). Michael- q)e addition of r-butyl (/7)-(p-tolylsulfinyl)ace-tate to crotonic ester with NaH in DMF has also been reported, but the enantiomeric excess of the desulfurized product is very low (12%). ... [Pg.523]


See other pages where Crotonate esters is mentioned: [Pg.100]    [Pg.173]    [Pg.112]    [Pg.224]    [Pg.966]    [Pg.105]    [Pg.34]    [Pg.57]    [Pg.235]    [Pg.85]    [Pg.373]    [Pg.136]   
See also in sourсe #XX -- [ Pg.127 ]




SEARCH



Croton

Crotonate

Crotonates

Crotonic

Crotonization

© 2024 chempedia.info