Claisen rearrangements retro

Evidence is the lack of a catalyst, the fact that the reaction is first order in the ether, the absence of crossover products when mixtures are heated, and the presence of the ally lie shift, which is required by this mechanism. A retro-Claisen rearrangement is... 

In the particular case in which the carbonyl group belongs to a carboxylic acid derivative, such as an ester (17) or an amide (18) (or other functional groups which may be converted into it by a FGI), then they may be disconnected according to the "orthoacetate-modification" of the retro-Claisen rearrangement (Schemes 7.7 and 7.8) developed mainly by Eschenmoser [7] and Ziegler [8], independently, in the synthesis of alkaloids, and Johnson in a very simple and yet highly stereoselective synthesis of squalene [9]. 

A cyclobutane with a carbonyl and a vinyl group in a cis-, 2-position readily undergoes a retro-Claisen rearrangement as soon as it is formed at room temperature by oxidation of the corresponding alcohol, e.g. formation of l.183... 

Retro-Claisen rearrangement The formyl bicyclo[2.2.2]octane 1 when heated with a catalytic amount of HO Ac at 110° rearranges to the vinyl ether 2, probably because of relief of the strain associated with the vic-quatemary carbon centers. This retro-Claisen rearrangement occurs rapidly at 0° in the presence of BF3 0(C2H5)2 (0.1 equiv.).10... 

Sometimes, aldehydes obtained by TPAP oxidations suffer in situ intramolecular transformations in substrates with a great predisposition to do so. Examples found in the literature include retro-Claisen rearrangements,108 dipolar additions on enals,106a and attack of malonates109 and indole rings11 on aldehydes. 

Boeckman Jr. RK, Zhang J, Reeder MR (2002) Synthetic and Mechanistic Studies of the Retro-Claisen Rearrangement 4. An Application to the Total Synthesis of (+)-Laurenyne. Org Lett 4 3891... 

The Claiscn rearrangement of allyl vinyl ethers is usually an irreversible reaction due to the energetic benefit of forming aC-O double bond. However, in strained bicyclic systems the retro-Claisen rearrangement (3-oxa-Cope rearrangement) of y,<5-unsaturated aldehydes has been observed32. Sometimes equilibrium mixtures of vinyl ether and carbonyl compound were found. For example, the ratio of the valence tautomers, bicyclo[3.1.0]hex-2-ene-6-cWo-methanal to 2-oxabicyclo[3.2.l]octa-3,6-diene, is approximately 7 333. Nevertheless this reaction was used in the preparation of a key intermediate in a prostacyclin synthesis34. 

The corresponding bicyclo[2.2.2]octene derivatives provided an equilibrium mixture (8 1) with only minor amounts of the retro-Claisen product36. The Diels - Alder adduct from diphenylful-vene and (Z)-hex-3-en-2,5-dione rearranged completely to the corresponding dihydropyran at 45°C in ethanol37. 

Formyl bicyclo[2.2.2]octane undergoes retro-Claisen rearrangement to a vinyl ether in the presence of BF3 Et20 at 0 °C (Eq. 49), but not with HOAc at 110 °C [94]. 

Type of reaction Rearrangement Reaction condition solid-state Keywords retro-Claisen rearrangement... 

For other facile retro-Claisen rearrangements see refs 48-51, for an example in the thia-Claisen rearrangement series, cf. ref 52. Flowever, it has been pointed out that the irreversibility of the Claisen rearrangement in the oxygen series is only attributed to the large stability difference between reactant and product which drives the equilibrium to the right52. 

The previously inaccessible hydroxypyranone (147) has been obtained from the acid-induced rearrangement of the epoxypyrone (146). The mechanism involves a retro-Claisen reaction (Scheme 10). 

Some nice chemistry has been reported on the Cope and retro-Claisen rearrangements of alkynyl three-membered rings. The gas-phase thermolysis of c/5-ethynyl(vinyl)oxirans, e.g. (120), gave cyclopropanecarboxaldehydes (122) via the strained intermediate (121). However, in liquid-phase thermolysis, both... 

Other examples of retro-Claisen rearrangement were observed in the aromatic quinoline series [30] and with bicychc systems [31, 32]. Some specific cases have been predicted by calculations to be endothermic [33, 34]. 

Calculations and low-temperature NMR experiments have been used to investigate the course of reactions of diphenylketene with dienes. While the reaction of cyclic (s-cis) 1,3-dienes such as cyclopenta- and cyclohexa-1,3-diene yield 2- -2 (Staudinger) products, the low-temperature experiments indicate initial formation of 4-1-2 (Diels-Alder) intermediates. For the open-chain reactants, 2,3-dimethyl- and 1-methoxy-1,3-butadiene, both product types are formed initially, with conversion of the Staudinger to the Diels-Alder over time, via a retro-Claisen rearrangement. 

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