Retro-Dieckmann

Besides the Michael addition-initiated domino reactions presented here, a multitude of other anionic domino reactions exist. Many of these take advantage of an incipient SN-type reaction (for a discussion, see above). In addition to the presented SN/Michael transformations [97, 98, 100], a SN/retro-Dieckmann condensation was described by Rodriguez and coworkers, which can be used for the construction of substituted cycloheptanes as well as octanes [123]. Various twofold SN-type domino... 

The same paper reports another route to 11-membered acetylenic lactones via an intramolecular retro-Dieckmann reaction (equation I). Thus treatment of 3 with... 

MARDi Michael addition-Aldolisation-Retro-Dieckmann... 

In another study, Buchanan and McLay (104) found that the equatorial oicy- ri clic ketotosylate 36S gave the seven-membered olefinic ester 367 while the,. axial isomeric tosylate 368 gave the seven-membered olefinic ester 371. Again, the reaction of the equatorial tosylate occurs through the fragmen- tation of intermediate 366. The transformation 368- 371 can be explained by the stereoelectronically controlled retro-Dieckmann fragmentation of 369 followed by the elimination of the tosylate group from 370. 

A method for the enantioselective synthesis of the ftmctionalised carbapenam core 38 from D-serine-derived pyrrolidines has been reported <03JOC187>. Disubstituted pyrrolidines, obtained from the retro Dieckmann reaction of azabicyclo[2.2.1]heptan-2-one-1-carboxylic acid methyl esters, have been used as starting materials to develop concise syntheses of all four stereoisomers of carbapenam-3-carboxylic acid methyl esters <03JOC2889>. The synthesis of 1-methylcarbapenams 39 by intramolecular attack of lactam nitrogen on a 77 -propargylpalladium complex has been reported <03JOC8068>. 

In Kozikowski s synthesis of showdomycin, treatment of the oxabicyclic 130 with bicarbonate induced a retro-Dieckmann reaction to reveal the highly substituted tetrahydrofuran intermediate 131, Eq. 93 [142]. 

Similarly, treatment of substrate 132 with sodium methoxide led to a retro-Dieckmann reaction to yield the interesting bicyclic ether 133 as a single isomer, Eq.94 [90]. 

The reversibility of the process means that cyclic 2-alkoxycarbonyl ketones can be cleaved by alkoxide in the retro-Dieckmann reaction, a process of synthetic significance (see Section 3.6.9.1). More recently, nonequilibrium conditions have been employed in the reaction and this may lead to a change in regioselectivity (see Section 3.6.3.3.3). 

The equilibrium character of the reactions described in this chapter means that the reverse processes also occur. The retro-Claisen, retro-Dieckmann and retro-Thorpe-Ziegler reactions are all known and can be synthetically useful. In some cases the substrate may have been formed by the same or similar forward reaction, whereas in others the substrate has to be formed by another process since the equilibrium lies completely on the side of the retro-reaction product. As in the case of the forward reaction, tandem reaction sequences can be constructed, often with the same types of preceding reaction as were described for the forward sequence. 

An acid-catalyzed retro-Dieckmann reaction converts the p-keto ketal (237) into (238a), which can be transesterified to the methyl ester (238b). ° No racemization occurs at the noncleaving ring junction, both enantiomers of (237) proceeding with retention of configuration (Scheme 100). 

As with the forward reaction, the retro-Thorpe-Ziegler reaction has found much less use than the retro-Dieckmann reaction. A Thorpe-Ziegler, retro-Thorpe-Ziegler sequence has been used to a-tetra-methylate the bisnitrile (239 Scheme 101). ... 

Dihydroxynaphthoyl-CoA synthase and Bad Dieckmann and retro-Dieckmann reactions... 

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