Enoates, arylation

An important extension of this work deals with the preparation of N-substituted l,4-dihydropyridine-3,5-diearboxylates. Tliirty examples have been deseribed (92SC3291). In most eases the reported yields (10-95%) are higher than those mentioned in the literature. Tire most signifieant results eoneern the synthesis of 1-aryl derivatives, whieh are hardly aeeessible by elassie methods. One should mention that the aminoeyelohexadiene 84 has been isolated as a by-produet when starting from ethyl A-benzylaminobut-3-enoate (Seheme 26). 

Wolff rearrangement of a-diazoketones to give ketenes or subsequent products is an often used synthetic procedure the scope and limitations of which are well established 13 390), so that only a few new features of this reaction need to be considered here. Concerning its catalytic version, one knows that copper, rhodium and palladium catalysts tend to suppress the rearrangement390). A recent case to the contrary is provided by the Rh2(OAc)4-catalyzed decomposition of ethyl -2-diazo-3-oxopent-4-enoates 404 from which the p,y-unsaturated esters 405 are ultimately obtained via a Wolff rearrangement 236). The Z-5-aryl-2-diazo-3-oxopent-4-enoates undergo intramolecular insertion into an aromatic C—H bond instead (see Sect. 4.1). 

With glyceraldehyde-derived enones and enoates, it has been found that addition of aryl or alkenyl copper reagents is almost independent of the enone geometry [24, 25]. In agreement with the modified Felkin-Anh model, Z enoates usually provide high levels of anti selectivity (Scheme 6.11). Hence, the Z derivative 64 reacted with complete stereochemical control, whereas the -enoate 64 gave a lower selectivity of 4 1 in favor of the anti-conjugate adduct [25]. 

The kinetics of reactions between aroylpyruvic acids, ArC0CH2C0C02H, and arylamines in toluene show evidence of several mechanistic features intramolecular carboxyl catalysis, and catalysis by a second molecule of nucleophile, either on its own, or in concert with an (external) carboxylic acid. An extended solvent study shows an increase in the efficiency of the aforementioned intramolecular carboxyl catalysis with decreasing polarity of the solvent.Hydrolysis of the related /3-keto esters, methyl 4-aryl-2-arylamino-4-oxobut-2-enoates [ArC0CH=C(NHAr)C02Me] in aqueous dioxane is subject to general acid catalysis. " ... 

Asymmetric arylation of chiral oxazolines has provided a versatile method for the arylation of enoates. For example, 104 was arylated with an aryllithium re-... 

New additions to the hetero Diels-Alder (hDA) approach to dihydropyrans include the reaction between enol ethers and 3-aryl-2-cyanoprop-2-enoates that under high pressure yields substituted 3,4-dihydro-2W-pyrans with high endo- and complete regio- selectivity. The products can be transformed into a wide variety of other compounds <02EJO3126>. 

Taylor, E.C., and Davies, H.M.L., Rhodium(II) acetate-catalyzed reaction of ethyl 2-diazo-3-oxopent-4-enoates. Simple routes to 4-aryl-2-hydroxy-l-naphthoates and P,y-iinsaliiralcd esters. The dianion of ethyl 4-(diethylphosphono)acetoacetate as a propionate homoenolate equivalent, Tetrahedron Lett., 24, 5453. 1983. 

A -Aryl-iV -phenylalkynylamidines are cycitzed to quinolines by treatment with hot PPA the main product is the 2-(A -methyl-yV-phenylamino)quino]ine but cyclization on to the other benzene ring may (xxur to some extent. 3-Phenyl-aminobut-2-enoate esters are cyclized (on to a ring-carbon) at or below room temperature by the application of Vilsmeier reagents. 

This method of diastereoselective cyclopropanation can also be used with reasonable success for the enantioselective entry to tropanes by a tandem cyclopropanation Cope rearrangement of the 2-diazobut-3-enoate with the (i )-pan-tolactone auxiliary group in the presence of N-( err-butoxycarbonyl)pyrrole (8.185). The product 8.186 was obtained by Davies and Huby (1992) with 69% ee. It can be transferred in three steps into 8-azabicyclo[3.2.1]octane-2-carboxylates (8.187), which are the parent compounds for the corresponding 3-aryl derivatives. The latter are valuable probes for studying the neurochemistry of cocain abuse (Carroll et al., 1992 Lewin et al., 1992 Abraham et al., 1992). 

Heterocycle openings. a,p-Epoxy silanes fiimish P-hydroxy silanes due to the attack of cuprate reagents at the a-carbon. The regioselectivity for the reaction of methyl ( J-4,5-epoxypent-2-enoate with arylcopper is dependent on the presence or absence of BF,. The S 2 pathway giving the a-aryl esters becomes significant with the added Lewis acid. The Sf 2 products are observed in the reaction of epoxy vinyl sulfoxides with... 

It is important to note that both aliphatic and aromatic vinyl ketones were viable substrates in which P-alkyl and P-aryl substitutions were tolerated. Diaryl alkynes, mono-aryl internal alkynes, nonaromatic internal alkynes, terminal alkynes, and free hydroxyl-bearing alkynes were all efficient participants. It should be mentioned that while ynoates were successful nucleophiles, enoate electrophiles were found to be poor participants in nickelotalyzed couplings. 

In the presence of TMSOTf, Bi(0Tf)3 4H20 or Pd(Ph3P)4, the acetates of MBH adducts, such as methyl 3-acetoxy-3-aryl-2-methylenepropanoates and 3-acetoxy-3-aryl-2-methylenepropanitriles, have been smoothly converted into methyl (2 )-2-(acetoxymethyl)-3-arylprop-2-enoates and (2 )-2-(acetoxy-methyl)-3-arylprop-2-enenitriles, respectively (Scheme 3.42). A remarkable reversal in stereochemical direction from ester to nitrile was observed and is consistent with earlier results. 

Hydrosilylations by complexed CuH have been applied to several substrate types (Scheme 1-17). As illustrated by the following examples, the stereochemical outcomes from both 1,2-additions (to aryl ketones and aryl imines ) and 1,4-conjugate additions (cyclic ketones, P-aryl and/or P-silyl enoates, and unsaturated lactones) can be controlled by these ligand-accelerated reactions. One of the key tricks to this chemistry is to take advantage of the tolerance of CuH complexes to alcohols and water.In fact, several methods rely on the presence of a bulky alcohol (e.g., t-BuOH) to significantly enhance reaction rates. It takes relatively little added alcohol (volume-wise) to accelerate the hydrosilylation, usually on the order of 1-3 equivalents. The role of this additive is usually ascribed to the more rapid quenching of an intermediate copper alkoxide or enolate, which necessarily generates a copper alkoxide, an ideal precursor to rapid reformation of CuH in the presence of excess silane. Thus, the rate increase is presumably due to... 

In addition to the preceding methods that involve functionalization of an enone or enoate p-carbon with an alkyl or aryl functionality, methods for the nickel-catalyzed reductive aldol functionalization of enoates have also been developed (Scheme 3-81). Using triethylborane as the terminal reductant with Ni(cod)2 as catalyst, reductive aldol reactions proceed to give syn aldol adducts. An unusual role of phenyl iodide as a promoter for the process was found in this study. Intramolecular reductive aldol additions utilizing Ni(acac)2 as catalyst and diethylzinc as the terminal reduetant were also described. ... 

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