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Preparation and Intramolecular [2+2]-photocycloaddition of 1,5-dihydropyrrol-2-ones and 5,6-dihydro-1H-pyridin-2-ones With C-, N-, and O-linked Alkenyl Side Chains at the 4-position

Preparation and Intramolecular [2+2]-photocycloaddition of 1,5-dihydropyrrol-2-ones and 5,6-dihydro-1H-pyridin-2-ones With C-, N-, and O-linked Alkenyl Side Chains at the 4-position

Dominik Albrecht, Birte Basler, Thorsten Bach

J Org Chem. 2008 Mar 21;73(6):2345-56.

PMID: 18302416

Abstract:

The 1,5-dihydropyrrol-2-ones 2, 6, 9, and 11 were prepared from methyl tetramates (1a-c), N-Boc-protected tetramic acid (3), or N-Boc-protected tetramic acid bromide (7) in short reaction sequences and in very good overall yields. The homologous 5,6-dihydro-1H-pyridin-2-ones 16, 18, 20, 21, 23, and 27 were prepared along analogous routes starting from piperidin-2,4-dione (19) or from its N-tert-butyl derivative 15. Optimized conditions for the [2+2]-photocycloaddition include the use of dichloromethane as the solvent and an irradiation with a mercury low-pressure lamp (lambda = 254 nm). Upon applying these conditions at ambient temperature, the corresponding intramolecular photocycloaddition products 28-37 were obtained in good yields (52-79%) and with perfect diastereoselectivity. The constitution and configuration of the products was elucidated by NMR-spectroscopy. For the O-tethered substrates 2a and 20, a strong decrease of the photocycloaddition rate with temperature was observed. The effect was less pronounced for N- and C-tethered substrates 6, 9, 23, and 27. The use of a chiral complexing agent to achieve enantioselective reactions appears viable. Complexing agent (-)-38, however, is not suited because of its instability at lambda = 254 nm.

Chemicals Related in the Paper:

Catalog Number	Product Name	Structure	CAS Number	Price
LS7931247	N-(Boc)-6-fluoroindole-2-boronic acid			Price

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