[66064-57-1] · C6H12N2 · Methacrolein Dimethylhydrazone · (MW 112.174)
(electron-rich 1-azadiene reacting with electron-poor alkenes to yield Diels-Alder adducts1-5)
Physical Data: bp 40-42 °C/20 mmHg.
Solubility: sol most organic solvents.
Preparative Methods: conveniently prepared either by the direct treatment of N,N-Dimethylhydrazine with Methacrolein or by a Hoffmann cleavage of the pyrazolinium iodide also obtained from methacrolein (eq 1).1-5 These methods have been successfully applied to the preparation of various a,b-unsaturated hydrazones (Table 1).
Handling, Storage, and Precautions: the compound darkens when kept at rt; however, it can be kept for long periods in the refrigerator without decomposition.
Methacrolein dimethylhydrazone reacts as an electron-rich diene in Diels-Alder reactions with alkenes bearing electron-withdrawing groups (eqs 2 and 3).1,5
The diene is moderately reactive and best results are obtained with more reactive dienophiles (eqs 4 and 5).1,6,7
Dimethyl maleate was isomerized to the more stable dimethyl fumarate under these conditions and, therefore, both dienophiles yielded the trans adducts. Reductive cleavage of the N-N bond was readily effected by Zinc-Acetic Acid to yield substituted piperidines.
Pyridines could not be obtained by reacting a,b-unsaturated hydrazones with alkynic dienophiles.6 However, they were readily obtained by reaction of methacrolein dimethylhydrazone with alkenic dienophiles bearing a nucleofugal group (eq 6)3 or with an allenic dienophile (eq 7).5
Methacrolein dimethylhydrazone and related 1-azadienes have been extensively used for the preparation of aza- and diazaanthraquinone derivatives.1,8 The cycloaddition reaction is highly regioselective (eqs 8 and 9).
Only few examples of intramolecular cycloadditions involving a,b-unsaturated hydrazones have been described.9
Only one example of a reaction of methacrolein dimethylhydrazone with a chiral dienophile has been reported (eq 10).10
Also it has been recently shown that the replacement of the dimethylamino group by a chiral pyrrolidine gives a 1-azadiene which cycloadds to cyclic dienophiles with high facial selectivities (eq 11).11 However, this diene did not react with dimethyl fumarate or acrylic derivatives.
Université Catholique de Louvain, Louvain-la-Neuve, Belgium