Photochemical reactions of prop-2-enyl and prop-2-ynyl substituted 4-aminomethyl- and 4-oxymethyl-2(5H)-furanones

Compounds with a heterocyclic 9-oxatricyclo[5.3.0.01,5]decan-8-one skeleton were synthesized by intramolecular [2+2] photocycloaddition reactions of the title compounds (λ= 254 nm, Et2O or MeCN as the solvent). Starting from various substituted 4-(prop-2-enylaminomethyl)-2(5H)-furanones, products 5, 9, 18, 21, 23, 24 were obtained, which bear a nitrogen atom in position 3 of this skeleton within a pyrrolidine ring. The Boc or Cbz groups represent suitable nitrogen protecting groups, which were compatible with the irradiation conditions and which can be easily cleaved. In an analogous fashion an oxygen (product 22) and carbon substituent (product 25) could be implemented at position 3 of the product if the starting material was appropriately chosen. The prop-2-ynyl substituted substrates did not produce a [2+2] photocycloaddition product but rather underwent a cyclization to spiro products 11 and 13.