Vinylogous -keto esters

Aryllead triacetates react with a mixture of isomeric vinylogous keto esters re-giospecifically at C-1. In the synthesis of alkaloids such as ( )-mesembrine [39] and ( )-lycoramine [38], the central quaternary carbon center was installed by this electrophilic arylation reaction (Scheme 13.11). 

In this reaction organometallic compounds incapable of existence in high concentration are formed and utilized immediately. When an aide hyde or ketone is condensed with a halo ester the product is a fi-bydroxy ester. Sometimes dehydration occurs to give olefinic esters directly (method 19). The use of an ester as the carbonyl compound leads to /3-keto esters (method 234). The halo esters most commonly employed are of three types XCHjCOjCjHj, RCHXC02CjHj, and R CXCO CjH,. Vinylogous halo esters, such as y-bromocrotonate, and certain benzyl halides have been used with variable success. 

Ceccherelli, P., Curini, M., Epifano, F., Marcotullio, M. C., Rosati, O. Vinylogous Wolff rearrangement of 3,Y-unsaturated a-diazo- 3-keto esters a novel method for the preparation of substituted malonates. Synth. Common. 1995, 25, 301-308. 

Cleavage of ft-keto esters. P-Keto and vinylogous /3-keto esters are cleaved in high yield ( 95%) when refluxed with 5 eq. of this base in o-xylene for 6 hr. ... 

A general procedure for the preparation of keto-aldehydes (8) from cycloalkanones and their conversion into pyridines (9) has been reported. 4 Vinylogous silyl esters (6) are readily prepared from cycloalkanones and these, by reaction with allylic Grignard reagents, followed by hydrolysis, yield alkenes of type (7). The latter compounds are converted into the keto-aldehydes (8) by Pd / -catalysed oxygenation. 

Enaminones are compounds containing the system N—C=C—C=0. They are mono enamines of 1,3-diketones (vinylogous amides) or enamines of 3-keto esters (vinylogous urethanes). Their unique properties and the versatility of their applications in organic synthesis follow from the system Na Cb=Cc—Cd=Oe, which is tridentate (sites a, c, and e) toward electrophiles and bidentate (sites b and d) toward nucleophiles. This makes possible a wide variety of reactions, but with such a multiplicity of sites vulnerable to attack, reactions are sometimes unpredictable and can be unexpectedly complex. 

The spectrometric and chiroptical properties of vinylogous urethane derivatives of L-alanine and L-phenylalanine methyl esters (70) can be ascertained from the reaction of a-amino acid esters with cyclic ) -keto esters (Tortorella and Tangari, 1973). These chromophores show strong uv... 

The Pictet-Spengler reaction has been utilised in a three-component reaction between iV-(2-aminoethyl)pyrroles, enals and keto esters (Scheme 8.29). This reaction afforded chiral pyrrolopiperazines. Vinylogous reactivity of 2-vinyl pyrrole has been utilised in the formal [2 + 2] cycloaddi-tion, which proceeds via Michael addition followed by cyclisation. ... 

Later, Melchiorre and coworkers accomplished a challenging direct vinylogous aldol reaction of 3-methyl-2-(yclohexen-l-one with a-keto esters utilising a bifunctional primary amine-thiourea. Catalyst 48 based on the (l/ ,2/ )Kiiphenylethylene-l,2-diamine backbone combined with benzoic acid as cocatalyst promoted the reaction by means of a concomitant activation of both reacting partners (see TS in Scheme 19.55), the ketone via dienamine catalysis and the ester via hydrogen-bonding interactions (Scheme 19.55). 

General Synthesis and Reactions of Esters Synthesis of Diesters Synthesis of Hydroxy-esters Synthesis of Keto-esters Synthesis of Unsaturated Esters Synthesis of Aromatic Esters Synthesis of Thioesters Synthesis of Vinylogous Esters... 

As shown in Fig. 8, the Ni2-lb complex was applicable to broad range of catalytic asymmetric reactions under simple proton transfer conditions [19-30]. As donors in direct Mannich-type reactions, not only a-nitroacetates, but also malonates, p-keto esters [22], p-keto phosphonates [23], and a-ketoaniUdes [24] gave excellent enantioselectivity and diastereoselectivity. It is noteworthy that the Ni2-lb complex also promoted vinylogous direct catalytic asymmetric Mannich-type reaction of an a,p-unsaturated y-butyrolactam, giving synthetically versatile functionalized a,p-unsaturated y-butyrolactam in 99% ee [25]. Because the Ni2-lb... 

The unified highly convergent total and formal syntheses of ( + )-macro-sphelides B (441 X = O) and A (441 X = a-OH, p-H), respectively, have been described (483). Key features of the syntheses include the concise synthesis of the optically active S-hydroxy-y-keto a, 3-unsaturated acid fragment 442 via the direct addition of a fra/i.s-vinylogous ester anion equivalent to a readily available Weinreb amide, and the facile construction of the 16-membered macrolide core of the macrosphelide series via an INOC. 

The synthetic usefulness of dioxin vinylogous esters as p-keto vinyl cation equivalents was demonstrated by a variety of reductive and alkylative 1,3-carbonyl transpositions.5 7 Regioselective alkylation and hydroxylation at the a -position (and, in some cases, at the y-position)8 9 further extend the usefulness of 1,3-dioxin vinylogous ester templates in organic synthesis. 

After purification, the dimethyl 1,3-dioxinone unit of 2 was hydrolysed with mild base to furnish the P-keto acid. Acidification then brought about lactonisation to the enolised p-keto lactone 1. To facilitate work-up and isolation, the latter was converted to the vinylogous ester 24 with potassium carbonate and dimethylsulfate in acetone. Mild acid hydrolysis of 24 with 0.1 N H2S04 in EtOAc eventually furnished (-)-ACRL toxin 1 in good yield after six days, completing this very elegant and beautifully crafted synthesis. 

Malonate esters and vinylogous malonates, as well as 1,3-diketones, readily undergo diazo transfer. In addition, the less acidic -keto phosphonates (138 equation 55) ° and p-keto sulfones (140 equation 56) have been shown to participate in this reaction. 

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