PHOTOCHEMISTRY OF ALPHA-BIS(METHOXYIMINO)ALKANES

The photochemistry of the alpha-bis(methoxyimino)alkanes 1-5 and the, structurally related, conjugated dihydro(methoxyimino)isoxazoles 6 and 7 was studied. Triplet-photosensitized irradiation of 1-7 leads only to stepwise E-Z isomerization. Photostationary-state (pss) ratios for 1, 6 and 7 are reported for the various applied triplet sensitizers. Direct irradiation with 254 nm leads to both E-Z isomerization (which is the dominant reaction) and formation of products resulting from initial N-O homolysis of the excited singlet pi-pi* state. Mechanisms for the formation of the various products are proposed and the relative importance of the various steps is indicated and discussed. For the alpha-bis(methoxyimino)alkanes 1 and 3, only the (E,Z)-isomer undergoes N-O homolysis. With the (methoxyimino)isoxazolines 6 and 7, only the exocyclic N-O bond exhibits homolysis and not the strained endocyclic bond.