Diels-Alder reaction dimethyl hydrazones

Electron-deficient allenes also undergo hetero-Diels-Alder reactions. N,N-Dimethyl-hydrazones 193 reacted with allenedicarboxylate 110a in refluxing acetonitrile to give 2-carboxy-3-pyridineacetic acid diesters [157]. 

Thus, Ghosez et al. were successful in showing that A,iV-dimethyl hydrazones prepared from a,/3-unsaturated aldehydes react smoothly in normal electron demand Diels-Alder reactions with electron-deficient dienophiles [218, 219]. Most of the more recent applications of such 1-aza-l,3-butadienes are directed towards the synthesis of biologically active aromatic alkaloids and azaanthra-quinones [220-224] a current example is the preparation of eupomatidine alkaloids recently published by Kubo and his coworkers. The tricyclic adduct 3-19 resulting from cycloaddition of naphthoquinone 3-17 and hydrazone 3-18 was easily transformed to eupomatidine-2 3-20 (Fig. 3-6) [225]. 

The investigation of the Diels-Alder reaction of 2-substituted-a,/5-unsaturated hydrazones in a concentrated solution of LiNTf2 in MeCN revealed a spectacular rate increase when the reaction of 80 with A-phenylmaleimide (81) was run in this media (2.5 M LiNTf2-MeCN) (Sch. 40). These conditions also enable cycloadditions to be performed with less reactive dienophiles such as dimethyl fumarate or malate such cycloadditions result in stereospecific cyclizations [90]. 

The preparation and a Diels-Alder reaction of (lE)-l,3-dimethoxybutadiene have been described. Dimethyl maleate and dimethyl fumarate each react with the hydrazone (92) to give the adduct (93) reductive cleavage of the N-N bond then gives the tetrahydropyridine (94) (Scheme 50). ... 

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