The photogeneration and cycloaddition reactions of tert-Butyl subtituted quinone methides
LE3 .A278 2022
Bachelor of Science
Two phenols, 6-tBu-2-hydroxybenzyl alcohol (22) and 4,6-di-tBu-2-hydroxybenzyl alcohol (23), were prepared using a sodium borohydride reduction, in yields of 93% and 75%, respectively. After attempts to purify 23 through recrystallization from hexanes with no success and a low yield (11%), this compound was not used further. Irradiation of 22 in methanol containing solutions gave the corresponding methyl ether 26 in high yields. Irradiation of 22 in solutions containing electron-rich dienophiles gave high yields of the expected [4+2] products, indicating that a quinone methide (QM) intermediate was formed. Product studies were carried out in different solvent mixtures containing varying amounts of water, methanol, and acetonitrile and it appears that the reaction taking place was largely solvent independent. For the formation of the [4+2] products, the presence of water actually hampered the reaction. Fluorescence studies showed that the addition of small amounts of water to an acetonitrile solution of compound 22 led to some quenching, however addition of more water did not lead to further quenching. This supports a reaction mechanism where photodehydration takes with no solvent assistance to give a quinone methide intermediate.
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