Since excellent synthetic procedures for the preparation1,2 o f pure mixed anhydrides of formic acid and other carboxylic acids are now available, it appeared worthwhile to investigate the reactivity of these anhydrides towards aldehydes, which might lead to a synthesis o f the hitherto unknown mixed alkylidene dicarboxylates of formic acid and other carboxylic acids.

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Acyclic 1 -cyanobutadienes (2) having a second electron-withdrawing substituent at C-1 behave towards tetraalkoxyethenes (1) like equally substituted simple olefins. The normal product is a [ 2 + 21, not a [4 + 21 cycloaddition product. The correspondence in reactivity of these electron-poor olefins and butadienes towards the nucleophilic tetra-alkoxyethenes is further exemplified by the similarity of substituent effects on the cycloadditions. A possible explanation is given.WE have shown previously2j3 that under thermal conditions tetra-alkoxyethenes (1) give [2 + 21 cycloaddition products with electron-poor olefins having two electron-withdrawing groups at one of the olefinic carbon atoms. However, when one of the electron-withdrawing substituents in the electrophilic olefin is an acyl residue, as in a-cyano-ap-unsaturated carbonyl compounds, only [4 + 21 cycloaddition products arise.In connection with these results we have now investigated the behaviour of tetra-alkoxyethenes towards