Alkoxycarbonyl group

Pyridazinecarbohydrazides are prepared in the normal way from an ester or acid chloride and hydrazine or a substituted hydrazine, generally in good yields. Pyridazines with two ortho alkoxycarbonyl groups give cyclic hydrazides with hydrazine, which are pyridazinopyridazines. 

The alkoxycarbonyl group activates the N — N bond, so that a racemization-free reductive cleavage by treatment with a large excess of lithium in liquid ammonia is possible (sec procedure below). This method is not suitable for hydrazines containing a benzylic C-N bond, because it is cleaved under the reducing conditions. 

In the hydrogenation of 3-substituted itaconate ester derivatives by rhodium-dipamp, the alkoxycarbonyl group at the stereogenic center also exerts a powerful directing effect, comparable to that induced by OH in the kinetic resolution of (a-hydroxyethyl)acrylate, leading to a high enantiomer-discriminating ability up to feR fes = 16 1 (Table 21.18, entry 5) [64]. 

Under oxidation conditions, a C—C double bond can be functionalized by either two alkoxycarbonyl groups or one alkoxycarbonyl group and one heteroatom. As shown in Scheme 4.14, two ester groups are successfully introduced to styrene in an enantioselective manner, producing a phenylsuccinic ester using a Pd/MeO-BIPHEP complex. mcw-Diols are converted into cyclic ethers in an asymmetric manner when catalyzed by Pd/chiral bisoxazoline. Intramolecular aminopallada-tion followed by carbomethoxylation gives an cyclic amino ester in moderate ee when catalyzed by a Pd/bis(isoxazoline) complex. " ... 

However, the real breakthrough came with the drastically facilitated preparation of 1-cyclopropylcyclopropanol (15) from methyl cyclopropanecarboxylate (19) applying the transformation of an alkoxycarbonyl group into a cyclopropanol fragment with ethylmagnesium bromide in the presence of Ti(zPrO)4 as developed by Kulinkovich et al. [13]. The optimized conversion of the alcohol 15 to the bromide 16 and its dehydrobromination makes the alkene 1 available in synthetically useful quantities of 40 -55 g within one week (Scheme 3) [ 14]. This sequence is also applicable to prepare substituted, especially spirocyclopropane-annelated, bicyclopropylidenes [ 14a]. 

A solution to this problem was found by using (4Ry 5S)-4,5-diphenyloxazoli-dine-2-one (100) [63] which turned out to be a suitable chiral ammonia equivalent permitting to achieve good diastereoselectivities with respect to the ste-reogenic center a to the alkoxycarbonyl group especially with 2 -substituted... 

The 2,3-double bond of compound 145 can be dibrominated with bromine <1982AP761>. The reaction is an analog of the dibromination of 126 described in Section 8.06.5.3. The 2-bromination of 152 to give 153 (Equation 6) was claimed to be a radical reaction, but is more likely to be an electrophilic attack, as a base catalyst was used and the reaction needed the presence of a 2-alkoxycarbonyl group to proceed <1984H(22)2789>. In a similar way, the a-carbons of dihydrooxazin-2-ones and dihydrooxazin-3-ones can also be deprotonated and then reacted with electrophiles these reactions are described in Section 8.06.6.5. 

These results can be interpreted as the sum of the steric effects of the different substituents as depicted in 41. The effects of the two substituents R and phenyl more or less cancel each other out and what remains is the shielding effect of the alkoxycarbonyl group. Thus, a possible un-directing stereoelectronic effect by an electrophilic substituent which is perpendicular to the plane of the enolate (see COOCH3 in 41) has not been observed and instead substitution takes place from the less shielded side. 

The IV-sulphinyl group in Davis sulphinimines 58a and 58b117, in analogy to the alkoxycarbonyl group in 56, hampers ring closure to /3-lactam, as independently reported by Staas and coworkers118 (equation 36) and Soloshonok and coworkers119 (equation 37). 

Deprotonation of methylene groups containing two electron-withdrawing alkoxycarbonyl groups with an appropriate base easily converts them into their corresponding enolate anions. These enolate anions are able to attack carbon electrophiles to form new C —C bonds. One of the important applications of this reaction is to construct small carbocyclic rings, in particular cyclobutanes. For example, intermolecular condensation of l,3-dibromo-2,2-dimethylpropane (1) and the dipotassium salt of diethyl malonate (2) gives diethyl 3,3-dimethylcyclobutane-l,l-dicarboxylate (3).18... 

Cyclopenta[c]quinolizines (51) reacted with acetylenic esters in boiling nitrobenzene to give cyclopenta[cd]cycl[3,3,3]azines (52). Other media were found to be ineffective, even in the presence of palladium-charcoal. The alkoxycarbonyl groups of the esters were readily removed by alkaline hydrolysis followed by vacuum pyrolysis of the resulting... 

Cyano and alkoxycarbonyl groups are favorable in this respect and propeneni-trile and methyl 2-methylpropenoate can be polymerized with sodium amide in liquid ammonia. Ethenylbenzene and 2-methyl-1,3-butadiene undergo anionic polymerization under the influence of organolithium and organosodium compounds, such as butyllithium and phenylsodium. 

Quinuclidinecarboxylic esters easily undergo saponification. This process is especially easy for a-alkoxycarbonyl groups.134 Aqueous solutions of ethyl 3-ethoxycarbonylmethylquinuclidine-2-carboxylate... 

Some of the above reactions have been shown to follow a stereoselective course.157 The 3-ethylidenequinuclidine (115) is formed through an intermediate complex which has the methyl and a-methylene groups separated as far as possible. The stereochemistry of the 3-alkoxycarbonylmethylenequinuclidines (116) is determined by the interaction of the ring nitrogen atom with the alkoxycarbonyl group which leads to the isomer with these two groups on the same side of the double bond. 

An interesting method for the introduction of substituents into the 2-position of the quinuclidine ring starting from 3-substituted A2-dehydroquinuclidines (126) has been described.47 By the reaction of methyl J2-dehydroquinuclidine-3-carboxylate (130) with iso-propylmagnesium bromide, 1,4-addition with formation of 2-iso-propyl-3-methoxycarbonylquinuclidine (131) took place instead of a sterically hindered Grignard reaction at the alkoxycarbonyl group. 

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