To conjugated esters

Other nucleophiles add to conjugated systems to give Michael-type products. Aniline derivatives add to conjugated aldehydes in the presence of a catalytic amount of DBU (p. 488). Amines add to conjugated esters in the presence of InCla, La(OTf)3, or YTb(OTf)3 at 3kbar, for example, to give P-amino esters. This reaction can be initiated photochemically. An intramolecular addition of an amine unit to a conjugated ketone in the presence of a palladium catalyst, or... 

Table 9.26 1,4-Additions of allenyltitanium reagents to conjugated esters.

A wider range of cyclizations occurred to conjugated ester dipolarophiles. Thus, (221) underwent thermolysis to the corresponding carbonyl ylide, which cyclized to give mainly bridged cycloadduct.122 The homologous oxirane with a five-carbon chain was also studied and gave only the transfused product (222) in 73% yield at 55% conversion. 

For diastereoselective nitrone intramolecular cycloaddition to conjugated esters, see R. Annunziata, M. Cinquini, F. Cozzi and L. Raimondi, Tetrahedron Lett., 1988, 29, 2881. 

Conjugate addition of alcohols to conjugated esters, using ceric ammonium nitrate and LiBr, gave the corresponding a-bromo-p-alkoxy ester. ... 

In many of these cases, both the enolate anion and substrate can exist as (Z) or (E) isomers. With enolates derived from ketones or carboxylic esters. The (E) enolates gave the syn pair of enantiomers (p. 166), while (Z) enolates gave the anti pair. Nitro compounds add to conjugated ketones in the presence of a dipeptide and a piperazine. ° Malonate derivatives also add to conjugated ketones, and keto esters add to conjugated esters.Addition of chiral additives to the reaction, such as metal-salen complexes,proline derivatives, or (—)-sparteine, ... 

Thiophenol and butyllithium (lithium phenylthiolate) adds to conjugated esters. Similar addition is observed with selenium compounds RSeLi. 

Aliphatic alcohols are converted to a symme-RCOOCH2R) by oxidation with PCC on aluminum without solvent. Oxone in aqueous methanol also converts aryl aldehydes to the corresponding ester. Ally lie alcohols are converted to conjugated esters with Mn02, NaCN in methanol-acetic acid. Primary alcohols are oxidized to the methyl ester with tri-chloroisocyanuric acid in methanol. This reagent also converts diols to lactones. 

Sakai and co-workers [38] studied the additions to conjugate esters protected with a cyclic diol as a chiral auxiliary. The ester is protected with enantiomerically pure ( R2R) rrfl/js-cyclohexane diol (see Table 4, entry 7). Addition of phenyl Grignard reagent, catalyzed by Cul, produced a moderate yield (50%) of a mixture of the two diastereomers (prochiral carbon R/5 = 78% 22%) with a d.e. of 55%. In contrast, the authors also reported that addition of the phenyl lithium cuprate gave 94 6 ratio with the major product having the S-configuration for the prochiral carbon. Because of the differences in the structures of the complexes, attack from the lithium cuprate comes from the Re-face, whereas attack from the copper-Grignard comes from the Si-face. 

A combination of TMEDA and MCjSiCl makes benzylic copper reagents more stable and permits their applications to conjugate addition to a,P-unsaturated esters. Chelation control is manifested in the cuprate addition to conjugate esters by a trivalent phosphorus atom 8 bonds away. ... 

The nonconjugated trienic esters of linseed oil are rapidly isomerized to conjugated esters by treatment with the base in DMSO, DMF, or tetramethylurea (all about equally effective). Practically no conjugation occurs in butanol. 

Condensation reactions. Nitriles activated through coordination to Rh become nucleophilic toward aldehydes in DMSO such that p-hydroxy alkanitriles are formed at room temperature. The Rh complex also promotes transfer reaction of an organoborane to conjugated esters, and those with additional bonding opportunities cyclic structures may be erected. ... 

Michael-aldol reaction tandem. Addition of lithium benzenethiolate to conjugated esters in the presence of aldehydes is followed by an aldol reaction in a stereoselective manner. 

Oxidation of nitrogen and sulfur compounds. These oxidations serve to complete transformation of amines to hydroxylamines, hydrazones to nitriles, and p-amino esters to conjugated esters.- ... 

THF is essential for these reactions in its role as the hydrogen donor and supplies the requisite hydrogen atom. This feature was established by deuterium labeling studies. However, these radical-mediated reactions fail to add to conjugated esters and cyclohexene acceptors and require an aniline substituent for successful radical-mediated ring closure. A bridged ring example is illustrated in eq 11. ... 

Recently, Cobb and co-workers [110] developed the organocatalytic asymmetric intramolecular Michael reaction of nitronates to conjugated esters (Scheme 5.52). By... 

SCHEME 5.52. Intramolecular Michael reaction of nitronates to conjugated esters. 

Trost and coworkers [88] successfully extended the methodology to conjugated esters and amides under identical conditions (Scheme 19.54). 

An important synthetic route to conjugated esters involves a Wittig reaction with an aldehyde or ketone. Phenylacetaldehyde was converted to 3.6 in one example, allowing the synthesis of J. 7.4 This reaction involves conjugate addition of ammonia... 

Even weak nucleophiles such as amides can be added to conjugated esters if radical conditions are used, but the reaction also occurs with non-conjugated... 

The usual conjugate addition reactions of ammonia or amines to a,P-unsaturated esters can produce the amino acids discussed in this section. Just as amides were seen to undergo addition to conjugated esters in section 3.1.B (see 3.42 and 3.43), amine stabilized radicals add in a conjugate manner to a, )-unsaturated esters. The product of this reaction is an amino acid derivative. An example is the reaction of... 

Intensity studies on esters have been reported by many workers [13, 35—44, 45, 72, 73]. In general ester carbonyl bands are about twice as intense as the bands of comparable ketones. This applies equally to conjugated esters, which like the ketones show an intensification compared with the saturated examples. This assists the differentiation of esters and of their types, but it would be unwise to place too much reliance on it. 

Coupling Reactions. Trimethylsilylpropynylcopper adds to conjugated esters in a 1,6-manner if facilitated, giving mixtures of products dependent on the nature of the system. Addition to an unsubstituted ( )-dienoic ester gave an 8 2 mixture of aUenerpropynyl-substituted adducts (eq 1). 

Due to the relatively low reactivity of MeMgBr, its addition to conjugated esters provided mainly starting material. To overcome this problem, Feringa... 

NFSi also oxidizes iodide and bromide into electrophilic halogen. It was observed that the attack of iodide at the fluorine site of NFSi generates a reactive electrophilic iodine source. Indeed, in the rhodium-catalyzed 1,4-addition of organozinc to conjugated esters, the intermediate enol derivative reacted with electrophilic iodine obtained by oxidation of iodide coming from the iodoben-zene used for the preparation of the organozinc species (eq 55). ... 

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