Vinylogous carbonic esters

If vinylogous imidazole-A-carboxylates (route A) are treated with nucleophiles such as alkoxides or amines, the corresponding vinylogous carbonic esters or amides are obtained. While reaction of the vinylogous imidazole-TV-carboxylate with a thiol (route A) yields the addition product only, that of the corresponding imidazolium compound (route B) leads to the carbonic thioester in a substitution reaction [3]... 

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). 

Allylic displacements. New types of substrates for this (Ph3P)4Pd-catalyzed substitution are 3-allyloxyacrylic esters and (3-allyloxyvinyl sulfones. These vinylogous carbonates and sulfonates contain better leaving groups. 

Acyl carbonates (234), alkoxyquinones (235) as vinylogous esters, imino ethers (236), and diketene (237) react with ethyleneimine to give the corresponding acylated ethyleneimines. 

Entries 10 to 12 illustrate the use of organocopper conjugate addition in the synthesis of relatively complex molecules. The installation of a f-butyl group adjacent to a quaternary carbon in Entry 10 requires somewhat forcing conditions, but proceeds Transition Metals in ooc yie - I 1 Entry 11, the addition is to a vinylogous ester, illustrating the ability... 

Herein we will focus on the recent development of vinylogous [1] aldol reactions and their application in the synthesis of natural products [2-5]. In particular the synthesis of unsaturated esters through the vinylogous Mukaiyama aldol reaction is of great interest, since it provides rapid access to larger carbon frameworks and allows for a wide variety of transformations of the double bond (dihydroxylation, epoxidation, cuprate addition etc.). 

When a,/3-unsaturated esters are the target molecules, the use of a thioaldehyde or thioketone is advisable for the easy elimination of H2S from the intermediate thiol adduct. This strategy has been applied to thiolactams 94a and to thionolactones 94b, opening a route to vinylogous carbamates 95a143 and carbonates 95b144(equation 57). 

The vinylogous elimination to give alkenylcyclopropanes may also be effected via rt-allyl palladium complexes34,35. The palladium(0)-catalyzed substitution of allylic esters with stabilized carbon nucleophiles via 7i-allyl palladium derivatives stereospecifically proceeds with net retention (double inversion) of configuration. Thus, the chirality of an allylic substrate is transferred to resultant alkenylcyclopropanes in the intramolecular S J/ reaction via 7i-allyl palladiums (equation 21)36,3. ... 

Template reactions between malonaldehydes and diamines in the presence of copper(II), nickel(II) or cobalt(II) salts yield neutral macrocyclic complexes (equation 15).99-102 Both aliphatic102 and aromatic101 diamines can be used. In certain cases, non-macrocyclic intermediates can be isolated and subsequently converted into unsymmetrical macrocyclic complexes by reaction with a different diamine (Scheme ll).101 These methods are more versatile and more convenient than an earlier template reaction in which propynal replaces the malonaldehyde (equation 16).103 This latter method can also be used for the non-template synthesis of the macrocyclic ligand in relatively poor yield. A further variation on this reaction type allows the use of an enol ether (vinylogous ester), which provides more flexibility with respect to substituents (equation 17).104 The approach illustrated in equation (15), and Scheme 11 can be extended to include reactions of (3-diketones. The benzodiazepines, which result from reaction between 1,2-diaminobenzenes and (3-diketones, can also serve as precursors in the metal template reaction (Scheme 12).101 105 106 The macrocyclic complex product (46) in this sequence, being unsubstituted on the meso carbon atom, has been shown to undergo an electrochemical oxidative dimerization (equation 18).107... 

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. 

Vinylogous urethanes, j8-amino-acyclic esters are sensitive to hydrogenolysis. Rhod-ium-on-alumina, 5% Pd-on-carbon are used with success, but at below 100°C. ... 

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