Retro—Michael reaction

The yield of the cyclization step under the influence of a metal template can be increased when the corresponding dialdehyde 19 of the tetrapyrrole 16 is used. The reaction sequence is initiated by insertion of palladium(II) or nickel(II) into the tetrapyrrole to give 20 followed by Michael addition of one acrylaldehyde side chain to the other yielding the macrotetracycle 21 from which in a retro-Michael reaction acetaldehyde is eliminated to give 22. 

The combination of the carbonyl group and a / -hydroxyl group allows also the sugar to (a) dissociate in two smaller aldehydes, via the retro-Aldol reaction, or (b) eliminate the OH, via a retro-Michael reaction. 

Crossed reactions of the two aldehydes under phase-transfer catalytic conditions with the intermediate thioacetates, which can be isolated under controlled reaction conditions [14], leads to the formation of three products [13], as result of retro-Michael reactions (Scheme 4.18). In the case of the reactions involving crotonaldehyde, the major product results from the reaction of the aldehyde with the released thiolacetic acid, with lesser amounts of the expected crossed reaction products (Table 4.23). In contrast, the reaction of acrolein with the thioacetate derived from crotonaldehyde produces, as the major product, the crossed cycloadduct. These observations reflect the relative stabilities of the thioacetates and the relative susceptibilities of acrolein and crotonaldehyde to the Michael reaction. 

An intriguing tripartite interconversion of mitomycin A, albomitomycin A, and isomitomycin A is the result of a Michael and a retro Michael reactions [137]. The transformation of mitomycin A to albomitomycin A formally involves a cis addition, that from iromitomycin A, a tram addition. 

Conjugate addition reactions to the E-alkenoate proceeded fruitfully [293]. Remarkably, ketone enolates added to the alkenoate (Eq. 106) to afford the Michael adducts in the absence of the three fluorine atoms, the retro-Michael reaction dominates, because a ketone enolate is more stable that the ester enolate generated by the conjugate addition process therefore some special driving... 

If the carbon chain of the polyol contains 5 or more carbon atoms, a retro-MICHAEL reaction (RM) can occur from a 1-5 didehydrogenated species ... 

The cyclopropane ring can also be cleaved by a retro-Michael reaction. By appropriate positioning of the carbonyl groups by means of an intramolecular cyclopropanation, controlled ring opening to spiro systems (62),84 bicyclo[3.2.1]octanes (63)82 or bicyclo[2.2.2]octanes (64),82 has been achieved (equations 28-30). 

PCC is used to remove menthyl substituents working as chiral auxiliaries—from amines.306 The oxidation of menthylamines with PCC leads to P-aminoketones that, on treatment with base, suffer a retro-Michael reaction leading to free amines. 

We had several options to deal with the expected 1 1 diastereomeric mixture of 7 and 15, but none of them was in the end satisfactory. We had previously found that diastereomeric mixtures of certain other double Michael adducts (Figure 5) could be converted to thermodynamic mixtures upon treatment with base, presumably by a retro-Michael-Michael process.3 4 In the case of 7 and 15, the hope was that the two isomers could be equilibrated via a retro-Michael reaction to 17, internal bond rotation, and reclosure by a Michael reaction. Unfortunately, 7 and 15... 

One facile entry to intermediates possessing the y-lycorane skeleton involved the alkoxide-catalyzed cyclization of the isocarbostyril 34b, which was readily accessible by the N-alkylation of 34a, to provide the y-lycorane derivative 35 (104). The amino derivative 36 was available in three steps from the isocarbostyril 37 by a similar sequence of reactions, but several attempts to prepare the p-unsubstituted enone lactam 38 by this approach resulted in the loss of the N-(4-oxobutyl) appendage by a retro-Michael reaction and were unsuccessful. 

Phenoxypropanoic acid, 3-(phenylthio)propanoic acid, 4-phenylbutanoic acid and the corresponding ethyl and methyl esters have been pyrolysed between 520 and 682 K.10 Analysis of the pyrolysates showed the elimination products to be acrylic acid and the corresponding arene. The thermal gas-phase elimination kinetics and product analysis have been found compatible with a thermal retro-Michael reaction pathway involving a four-membered cyclic transition state. 

Scheme 3. Chirality transfer in a lithium phenylselenide induced domino-Michael-aldol-retro-Michael reaction (Jauch et al.).

Annulated pyridines are reported to be synthesized via a [4+2] cycloaddition involving oxazoles (Scheme 121 Table 10) <20010L877>. The reaction mechanism is classified as a domino process with an intramolecular Diels-Alder cycloaddition followed by a retro-Michael reaction. 

Treatment of 2,3-dihydrobenzopyran-4-ones 718 with base results in a retro-Michael reaction leading to the open-chain intermediate 719. An intramolecular aldol reaction followed by dehydration affords the biaryl intermediate 720, which recyclizes to form 7-hydroxy-677-benzo[c]chromen-6-ones (Scheme 177) <2002CC168>. 

Aldol Sensors and the Tandem Retro-Aldol-Retro-Michael Reaction... 

Scheme 4.11 Activation of a prodrug of the anticancer agent eto-poside via tandem retro-aldol/retro-Michael reactions catalyzed by antibody 38C2.

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