An improved procedure is described for preparing ß-trichloro- and ß-trifluoroacetyl derivatives of six simple enol ethers, in analytically pure form, high yield, and on an up to molar scale. The 4-alkoxy-1,1,1-trichloro [fluoro]-3-alken-2-ones 4a-c and 5a-c, thus obtained, are cyclocondensed with hydroxylamine hydrochloride (in pyridine, 35°C to afford the 5-hydroxy-5-trichloro[fluoro]methyl-4,5-dihydroisoxazoles 6 and 7 in high yield. With cyclic substrates, i.e. the trihaloacetyl dihydrofurans and -2H-pyrans 4d, e and 5d, e, a competitive rearrangement reaction gives 3-cyano-2-hydroxy-2-trichloro[fluoro]methyltetrahydrofurans and -2H-pyrans 8 and 9, respectively. Direct condensation to a dihydroisoxazole prevails at 0°C (> 85% for 4d, 5d), rearrangement to the cyano compounds at higher temperatures (65-70°C, > 70%). Under either condition, the respective heterocycle may be isolated in > 60% yield (except for 6e).

The preparation of 4-alkoxy-1,1,1-trichloro-3-alken-2-ones (enones), important synthetic tools for the heterocyclic synthesis, from cheap and easily accessible starting materials, is reported. The applications of the enones in the synthesis of isoxazoles, pyrazoles, pyrimidines and other heterocycles are also reported. This review was grouped into two main sections: (i) synthesis of 4-alkoxy-1,1,1-trichloro-3-alken-2-ones and derivatives and (ii) applications of 4-alkoxy-1,1,1-trichloro-3-alken-2-ones in heterocyclic synthesis.