1.2- Dihydropyridines, photoreactions

YOSHIRO KOBAYASHI AND ITSUMARO KUMADAKI [Sec. IV.D C. Photoreactions of 1,2-Dihydropyridines... 

The photoreaction of l-methoxycarbonyl-l,2-dihydropyridine gave a 2-azabicyclo[2.2.0]hex-5-ene compound,78 which was useful for the syntheses of N-substituted dihydropyridines.79 The latter showed peculiar transformations (Scheme 33).80 The bicyclic intermediate reacted with a cyclopenta-dienone. The product is a good precursor of azacyclobutene.81 The advantages of these syntheses are that a 2-azabicyclo[2.2.0]hex-5-ene is more stable and easier to deal with than the corresponding 1,2-dihydropyridine.82... 

Irradiation of the norbomadiene (41) produces the expected quadricyclane which undergoes a secondary photoreaction to give (42) by a (2 + 2 + 2) cyclisation followed by a [1.5]-hydrogen shift (Ivakhnenko et al). The efficient photodimerisation of the sterically hindered 1,4-dihydropyridine (43) in the solid... 

Photoreactions of Pyridones - Irradiation of 1-benzyl-1,4-dihydronicotina-mide (161) with the malonate derivative (162) affords a variety of products resulting from debromination and dimerisation. The dihydropyridine derivatives (163) are photochemically reactive in the solid phase. The formation of the products by irradiation has been shown to be a two step process affording the (2+2)-cycloaddition product (164) in the first step. Secondary irradiation of (164) then gives the cage compounds (165) in yields greater than 90%. 

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