A new synthesis of 2‐pyrones has been developed. Two molecules of α, β‐unsaturated acid chlorides (8, 12 and 18) condense, with loss of two molecules hydrogen chloride, to pairs of substituted 2‐pyrones (9 and 10, 13 and 14, 19 and 20) when treated with triethyl amine in chloroform or methylene chloride at room temperature. In the case of 18, two additional products were obtained, namely the resorcinol derivative 21 and traces of the 1, 3‐cyclobutanedione derivative 22. Under the same conditions the α, β‐unsaturated acid chlorides 8, 15, 18 and 41 were condensed with trichloroacetyl chloride to give 6‐trichloromethyl‐2‐pyrones (42, 43, 44 and 46). These 2‐pyrones are valuable intermediates for the synthesis of 6‐carboxy‐2‐pyrones and 6‐methyl‐2‐pyrones. A methyl group in β‐position of the α, β‐unsaturated acid chloride appears to be essential for the described condensations, for the acid chlorides 16 and 17 did not yield defined products and the acid chloride 40 reacted with trichloroacetyl chloride in a very low yield. It is considered that the described reactions proceed via the 1, 4‐addition of an acid chloride to a vinyl ketene or through the acylation of an intermediate anion by an acyl derivative as outlined in reaction scheme 1. The structures of the 2‐pyrones were confirmed by their spectroscopic properties, summarized in table 3, and by some of their chemical transformations.

The condensation of a, a-dichloropropionyl chloride (IVa) and of trichloroacetyl chloride (IVb) with a-chloropropionyl chloride (Ia) in the presence of triethylamine led to two acid chloride enol-esters, both as mixtures of cis-and trans-isomers, namely 1,2-dichloropropenyl a,a-dichloropropionate (Va) and 1,2-dichloropropenyl trichloroacetate (Vb).A mixture of triethylamine and trichloroacetyl chloride produced an oxidation-reduction reaction to give 48% 1, 2, 2, 2-tetrachloroethyltrichloroacetate (VIII) and 69% l-diethylamino-4,4,4-trichloro-l-butene-3-one (IX). Basic hydrolysis of I X led to 43% of glutaconic acid (XIII).Tripropylamine reacted in the same way with trichloroacetyl chloride to yield l-dipropylamino-2methyl-4,4,4-trichloro-but-l-ene-3-one (XIX) which was readily hydrolyzed in acid solution to a-trichloroacetyl-propionaldehyde (XX) .Vor kurzem haben wir [l] uber die Bildung von Carbonsaurechlorid-Enolestern

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Die Säurechloride (Ia) und (II) reagierten in Hexan in Gegenwart von Tri‐äthylamin (IV) in 23%iger Ausbeute zu einem 4:1‐Gemisch aus einem 1:1‐cis‐trans‐Gemisch des Esters (IIIa) und einem 1:1‐cis‐trans‐Gemisch von 1,2‐Dichlor‐propen‐(1)‐yl‐α‐chlor‐propionat.

Bei der Behandlung mit Triäthylamin in Chloroform oder Methylenchlorid entstehen durch Selbstkondensation aus Seneciosäurechlorid (I) als Hauptprodukte die Pyrone (II) (26% Ausbeute) und (III) (34%), aus Tiglinsäurechlorid (IV) die Pyrone (V) (31%) und (VI) (34%) und aus dem Zimtsäurechlorid (VII) die Pyrone (VIII) (20%) und (IX) (7%).neben dem "Tetrameren" (X) ( 17%) und Spuren von dem "Ketendimeren" (XI).