Phenyl-2-aza-l,3-pentadiene

Azadienes of this sort were studied simultaneously by Mariano et al., who reacted mixtures of (1 ,3 ) and (1E, 3Z)-l-phenyl-2-aza-l,3-pentadiene 275 with several electron-rich alkenes, e.g., enamines and enol ethers (85JOC5678) (Scheme 61). They found the (l ,3 )-stereoisomer to be reactive in this process affording stereoselectively endo 276 or exo 277 piperidine cycloadducts in 5-39% yield, after reductive work-up with sodium borohydride. The stereochemistry of the resulting adducts is in agreement with an endo transition state in the case of dienophiles lacking a cis alkyl substituent at the /8-carbon (n-butyl vinyl ether, benzyl vinyl ether, and 1-morpholino cyclopentene), whereas an exo transition state was involved when dihydropyrane or c/s-propenyl benzyl ether were used. Finally, the authors reported that cyclohexene and dimethyl acetylenedi-carboxylate failed to react with these unactivated 2-azadienes. 

The protic acid and Lewis acid-catalyzed [4 + 2] cycloaddition reactions of electron-rich alkenes with imines derived from anilines and aryl aldehydes constitute an extensively explored class of 2-azadienes capable of providing the products of a formaJ Diels-Alder reaction (equation 9).i5.27.i77 a useful extension of these studies and in efforts to increase the rate of the Att participation of simple 2-aza-1,3-buta-dienes in [4 + 2] cycloaddition reactions, Mariano and coworkers have examined the Lewis acid-catalyzed intermolecular reactions of (l ,3 )-l-phenyl-2-aza-l,3-pentadiene with electron-rich dienophiles, including enol ethers. Reductive work-up of the cycloaddition reactions provided the pro-... 

Phenanthrene o-quinodimethane, 55 Phenyl-2-aza-l,3-pentadiene, 258 6-Phenyl-5-azaazulene, 260... 

In efforts to increase the rate of simple 2-aza-1,3-butadiene participation in [4 + 2] cycloadditions, Mariano and co-workers investigated the related boron trifluoride etherate-catalyzed intermolecular cycloaddition reactions of (1 ,3 )- and (lE,3Z)-phenyl-2-aza-l,3-pentadiene with a... 

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