Retro-aldolisation

The problems associated with the basidty of fluoride are underscored by another example taken from Boger s synthesis of the Vancomycin CD and DE ring systems [Scheme 4,51],80 Attempted removal of the TBS group from 51.1 was accompanied by retro-aldolisation of the resultant p-hydroxyphenylalanine subunit to give 513 in 61% yield. Here again, buffering the reaction mixture with acetic acid suppressed the unwanted side reaction and gave the desired deprotected product 513 in 60% yield. 

Alkenes add photochemically to naphthalenes, normally to give products from 1.2 addition to the ring. In a report which appears to be a further example of this reaction Chow and co-workers reveal that Irradiation of mixtures of naphthols. or their methyl ethers, and acetyl acetone yield products derived from 1,2 addition of the enol form of the diketone to the naphthalene ring. Thus 1-naphthol gives the cyclobutanol (109) which retro-aldolises to the isolated product (110). However, the authors show that the excited state involved is In... 

As expected, pentoses react similarly to hexoses in the Maillard reaction, with the formation of 1- and 3-deoxyosones. However, the initial two-carbon fragment formed from the reaction of xylose with alanine is not the glycolal-dehyde expected from retro-aldolisation of the Amadori rearrangement product, but glyoxal, for reasons which are not clear. ... 

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

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