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The cyclization of trans-δ-hydroxy enones to cyclic mixed ketals routinely requires superstoichiometric strong acid. By operating under a photoisomerization regime, the cyclization of trans-δ-hydroxy enones proceeds under catalytic Brønsted acid to provide cyclic ketals or unsaturated spiroketals in a highly diastereoselective fashion. A one-pot, two-step protocol was thus developed to provide cyclic methoxy ketals with a free β-hydroxy group for future functionalization.
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Li et al. (2014) studied this question.
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