1). Acetals and ketals are hydrolyzed under neutral conditions, but very slowly. In this case, DDQ somehow accelerates (catalyzes) the neutral hydrolysis by behaving as a H-bonding acceptor (and indirectly, as a proton acceptor). If you draw the mechanism of acetal or ketal hydrolysis under neutral conditions with and without DDQ, you will immediately clarify by yourself, the role of the DDQ-water dimer via H-bonding. 2). The selectivity is due to the steric hindrance of the opposed spiro-ketal that inhibits the approach of the DDQ-water/H-bond dimer.
1). Acetals and ketals are hydrolyzed under neutral conditions, but very slowly. In this case, DDQ somehow accelerates (catalyzes) the neutral hydrolysis by behaving as a H-bonding acceptor (and indirectly, as a proton acceptor). If you draw the mechanism of acetal or ketal hydrolysis under neutral conditions with and without DDQ, you will immediately clarify by yourself, the role of the DDQ-water dimer via H-bonding. 2). The selectivity is due to the steric hindrance of the opposed spiro-ketal that inhibits the approach of the DDQ-water/H-bond dimer.
If you draw the mechanism of acetal or ketal hydrolysis under neutral conditions with and without DDQ, you will immediately clarify by yourself, the role of the DDQ-water dimer via H-bonding.
2). The selectivity is due to the steric hindrance of the opposed spiro-ketal that inhibits the approach of the DDQ-water/H-bond dimer.
If you draw the mechanism of acetal or ketal hydrolysis under neutral conditions with and without DDQ, you will immediately clarify by yourself, the role of the DDQ-water dimer via H-bonding.
2). The selectivity is due to the steric hindrance of the opposed spiro-ketal that inhibits the approach of the DDQ-water/H-bond dimer.
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