Ethyl crotonate

Having seen that the ordinary line notation of unbranched structures may be more or less equated with the structure itself we next turn to the case of branched structures. Just as an unbranched structure corresponds to a string of symbols, a branched structure has as its counterpart a tree. The nodes of the tree are part structure symbols and the edges are bonds. Thus 2,2,4-trimethylhexane may be represented by a number of trees, one of which is 

ACS Symposium Series American Chemical Society Washington, DC, 1977. 

One can define global part structures as was done above for ethyl crotonate and one notes that again there will be many tree representations per structure. 

The point of this, of course, is that, as is well known(l), trees (in particular binary trees) may be represented as lists. The above tree has a list representation, CH2(C(CH3)(CH3)CH3)CH(CH2CH3)CH3. Now this doesn t look too appealing to the chemists trained eye but CH3CCCH3)CCH3)CH2CH(CH3)CH2CH3 does. This is a list representation of the tree 

The following is a very brief introduction to the subject. We restrict ourselves to those aspects that are directly related to the problem of applying the theory of languages to organic chemistry. For a more complete introduction the reader is referred to a number of excellent texts.(2-5) 

CH3CH=CHCOOH + C2H5OH CH3CH=CHCOOC2H6 + h2o Michael, Ber., 33, 3766 (1900). 

A mixture of 50 g. (0.58 mole) of crotonic acid, 100 g. of absolute ethanol (p. 142), and 5 g. of concentrated sulfuric acid is refluxed for 5 hours and then poured into 1 1. of water. After thorough shaking 

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Required Ethyl crotonate, 22-8 g. V-bromosuccinimide, 35 6 g. carbon tetrachloride, 40 ml. 

Dissolve 22-8 g. of ethyl crotonate in 40 ml. of dry carbon tetrachloride and add 35 6 g. of. V-bromosuccinimide. Heat the mixture under reflux for three hours. Cool to o and filter off the succinimide which is insoluble in cold carbon tetrachloride. Now shake the filtrate with water in a separating funnel, separate and dry the carbon tetrachloride layer with sodium sulphate. Filter through a fluted filter-paper into a Claisen flask and distil... 

This procedure is generally applied to the esterification of highly sensitive acids, which might otherwise undergo isomerisation. Thus in the example given, no ethyl crotonate is formed. 

In a 3-1. flask provided with a reflux condenser are placed 114 g. (1.0 mole) of ethyl crotonate (Note 1), 460 ml. of 05%... 

Ethyl crotonate may be prepared readily from technical crotonic acid by action of sulfuric acid and alcohol. The checkers obtained 72% yield both by the ordinary procedure and by the method of azeotropic distillation. 

Muconic acid has been obtained in a variety of ways. The procedures that seem most important from a preparative point of view are by treatment of ethyl o ,5-dibromoadipate with alcoholic potassium hydroxide, by condensation of glyoxal (as the sodium bisulfite addition product) with malonic acid, by heating ethyl l-acetoxy-l,4-dihydromuconate (obtained by condensing ethyl oxalate and ethyl crotonate, acetylating, and reducing),and by oxidation of phenol with peracetic acid. ... 

Isayama described the coupling reaction of N-methylimine 157 and ethyl crotonate catalyzed by Co(acac)2 and mediated by PhSiH3 to produce Mannich product 158 in 82% with syn-selectivity (Scheme 41) [71]. The (i-laclam 159 was readily synthesized by heating 158. In 2002, Matsuda et al. reported cationic Rh complex [Rh(COD) P(OPh)3 2]OTf (1 mol%) as an active catalyst for the reductive Mannich reaction [72]. N-Tosylaldiminc 160 was coupled with methyl acrylate and Et2MeSiH (200 mol%) at 45 °C to give the b-amino ester 161 in 96% with moderate anti-selectivity 68%. 

Palladium(II) acetate was found to be a good catalyst for such cyclopropanations with ethyl diazoacetate (Scheme 19) by analogy with the same transformation using diazomethane (see Sect. 2.1). The best yields were obtained with monosubstituted alkenes such as acrylic esters and methyl vinyl ketone (64-85 %), whereas they dropped to 10-30% for a,p-unsaturated carbonyl compounds bearing alkyl groups in a- or p-position such as ethyl crotonate, isophorone and methyl methacrylate 141). In none of these reactions was formation of carbene dimers observed. 7>ms-benzalaceto-phenone was cyclopropanated stereospecifically in about 50% yield PdCl2 and palladium(II) acetylacetonate were less efficient catalysts 34 >. Diazoketones may be used instead of diazoesters, as the cyclopropanation of acrylonitrile by diazoacenaph-thenone/Pd(OAc)2 (75 % yield) shows142). 

The Michael-type reaction of an anion (generated from compound 77) with ethyl crotonate yielded the corresponding ester 78 in 82% yield (Scheme 19). Alkylation of compound 77 with benzyl bromide afforded derivative 79 in 85% yield. The attempted reactions of the anion with oxiranes and trimethylsilyl chloride did not lead to the expected substitution products and the starting oxadiazoles were recovered in 70-80% yields <2001ARK101>. 

Ethyl 2-bromocrotonate, CH3CH=C(Br)COOC2H5 (1). The reagent is prepared by bromination of ethyl crotonate followed by dehydrobromination with DBU. 

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