Acylfuran synthesis, furan

Very many naturally occurring 3-alkyl- or 3-acylfurans are now routinely synthesized by preparing a substrate for treatment with 3-furyllithium, itself made from 3-bromofuran according to Fukuyama, Tokoroyama, and Kubota, who used it to obtain pyroangensolide and fraxinellone.212 Equally, 2-lithiofuran is used for such natural products as the acetylenic furans from Alphonsea ventricosa213 and other compounds.214 For the synthesis of the sesquiterpenoid sponge-metabolite pleraplysillin-2 78, the lithiofuran 79 and therefore the bromofuran 80 was needed to secure the orientation a suitable preparation was devised for 80.215... 

The reaction of a-bromoacetals with trimethylsilylenolates catalyzed by titanium tetrachloride provides /3-alkoxy-y-bromoketones, which are useful furan precursors (Scheme 33) (75CL527). A new synthesis of acylfurans is exemplified by the formation of the 3-acetyl derivative (146) by heating the brdmoalkene (145) (78JOC4596). 2,2-Dimethyl-3(2//)-furanone (148) has been synthesized from 3-hydroxy-3-methylbutan-2-one treatment with sodium hydride and ethyl formate gave the hydroxymethylene derivative (147), which was cyclized and dehydrated to the furanone (148) with hydrochloric acid (Scheme 34) (71TL4891). O... 

Shaw and co-workers used a mixed Lewis acid approach to synthesize chiral furanmethanol derivatives from glycals. These compounds are important intermediates in the synthesis of many biologically significant compounds and serve as precursors for furanmethanes and 3-acylfurans. Reaction of a selectively protected 6-azido glycal with zirconium(IV) chloride and zinc(II) iodide gave the desired chiral furan selectively in 74% yield. 

Acylfurans, convenient intermediates for the synthesis of 2-substituted-3-hydroxypyridines, are s)mthesized by acylation of furans or by acylation of aromatic substrates with 2-furoyl halides. 3-Pyridinols (XII-272), pyrrolyl ketones, and pyrroyl ketimines are formed on treatment with ammonia. ... 

Acylfurans, ammonolysis, 665 frcm acylation of furans, 665 2-fnroyl halides, 665 used in synthesis of 2-alkyl (aryl)-3-pyridinols, 665 N-acylpyridones, rearrangement, 776... 

Exceptions due to steric and electronic reasons are known see (a) Carless, H. A. J. and Halfhide, A. F. E., Highly regioselective [2-i-2]-photocycloaddition of aromatic aldehydes to acylfurans, /. Chem. Soc., Perkin Trans. 1, 1081,1992 (b) Schreiber, S. L., Desmaele, D., and Porco, Jr., J. A., On the use of unsymmetrically substituted furans in the furan-carbonyl photocycloaddition reaction synthesis of a kadsurenone-ginkgoKde hybrid. Tetrahedron Lett., 29, 6689,1988. 

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