Unusual Spontaneous α→β Isomerization of Unsymmetrical Benzoins

The spontaneous thermal α→β benzoins isomerization of the some mixed aryl(furyl)benzoins takes place at the absence of bases. It is caused by two structure factors: the presence of halogen atom in para -site of the aryl moiety and the presence of Me 2 NN=CH-substituent in 5-site of the furane ring.