Oxazolyl aldehydes

In a similar manner, intramolecular cyclization of the O-stannyl ketyl derivatives 201 and 206, generated from the oxazolyl aldehydes 200 and 205, provides a facile method for the chiral synthesis of 3-hydroxy-2-(hydroxymethyl)-5-substimted-pyrrolidines 202 and 203 and the piperidine analogues 207 and 208 that can be successfully transformed into naturally occurring amino alcohols, (+)-bulgecinine 204 and (—)-desoxoprosopinine 209, respectively (Fig. 

Several oxazole-4-aldehydes have been described, while only one oxazole-2-aldehyde is known so far 2 4 they are fairly stable to oxidation by air. Since the oxazoles are not known to undergo Friedel-Crafts acylation, ketone substituents are introduced indirectly into the nucleus, either before the ring is formed40 332 391 or by modification of substituents already present.147 4-Acetyloxazoles are oxidized to the corresponding acids with sodium hypobromite.147 Both oxazolyl aldehydes and ketones form derivatives with hydroxylamine, phenylhydrazine, etc., as expected. 

This chelation-assisted C-H/olefin and C-H/acetylene coupling can be applied to a variety of aromatic compounds with a directing group such as ester, aldehyde, imine, azo, oxazolyl, pyridyl, and nitrile [7]. In this section, we describe the coupling reactions of aromatic carbonyl compounds with olefins using a transition metal catalyst. 

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