Tetraphenylporphin-photosensitized oxygenations of furan (19), 2-methylfuran (26), 2- ethylfuran (39), furfurylalcohol (24), 2-acetylfuran (40), 2-methoxyfuran (42), 2, 5- dimethylfuran (30), furfural (25) and 5-methylfurfural (41) in non-polar aprotic solvents yield the corresponding monomeric unsaturated secondary ozonides due to a (4+ 2)- cycloaddition of singlet oxygen to these furans. With the exception of the ozonide derived ...