AMrwi
-A highly selective synthetic route of general utility was devised for the preparation of 2'-hydroxycbakones 4. The procedure involves the regiochemical controlled reaction between bromomagncaium salts of mono and dibydric phenols 1 and variously substituted cinnamaldehydes 2 in aprotic apokr media and in the presence of a suitable basic additive. Application of this procedure to some naturally occurring chakoncs is reported. The crucial role of the additive is also emphasized. Although much effort has been expended on the synthesis of 2'-hydroxychalcones 4,'*' a direct method utilizing phenols as starting materials has not been reported. The best synthetic routes to 4 involve the Claisen-Schmidt condensation of 2hydroxyacetophenone-s with aromatic aldehyde-s' and the rearrangement of phenyl cinnamates.* However, both these methods do not permit a general application and occasionally call for substrates that are not readily available. Moreover, the Phenol Ciinamaldehyde 4a 62(82) 87-88 88-89" CtsHtxOx(224.25) Phenol 4Methoxycinnamaldehyde 58(85) 94-95 94O CtsHt,Os(254.27) 2Methylphenol Cianamaldehyde 2 68(85) 75-76 CtcHt,Os(238.27)' 3-Methoxyphenol Cinnamaldehyde Id 78(82) 104-105 107-108s C,JIH,,0s(254.27) 3Methoxyphenol 4-Mcthoxycinnamaldehyde L 60(85) 111-112 113-l 14b C,,H,,0,(284.30) 3Methoxyphcnol 3,4-Dimcthoxycinnamaldehyde Y 47(80) 152-154 156' C,,Ht,Os(314.32) 3-N.N-dimethylaminophcnol Cmnamaldehyde 80(90) 147-149 -C,,H,,N0,(267.31), bClrloropheno1 Cirmamaidehyde 2 48(88) 109-110 109-110~ C,,H,,ClOx(258.70) 3.4-Dimethoxyphcnol Cinnamaldehyde 60(92) 96-97 97-98' C,,H,,0,(284.30) 3-Hydroxyphenol Cinnamaldehydc tt 68(83) 139-141 142-143" C,,H,,0,(240.25) 3-Hydroxy4 methoxyphenol Cmnrmaldehyde R 60(80) 159-160 159" C,sH,,0.(270.27) 3-Hydroxy-5methoxyphenol Ciinsmsldehydc 41 66(91) 2&207 207" C16H,,0.(270.27) 'All products arc yellow or orange-yellow. bIsolated yields, values in psrentheses refer to yields based upon unrecovered starting phenol, not optimized.
CRecrystn solvent was benxene/hcxane in ali cases.