Cross-linked poly(N-bromoacrylamide) (PNBA) and poly(N- bromosuccinimide)
as the mild and efficient heterogeneous polymeric catalysts
were applied for selective deprotection of 1,3-dithianes and
1,3-dithiolanes to their corresponding carbonyl compounds. They
were also effective as a reagent in aqueous media. These methods
are very simple and the polymer catalysts could be recycled
several times. Deprotection of thioacetal and thioketal without enolizable
hydrogens proceeded very well to give only the corresponding
aldehyde and ketone in high to excellent yield. Nevertheless, in
the case of thioketals carrying enolizable hydrogens, deprotection
accompanied with the formation of a minor ring-expanded product
is observed. However, using the PNBA/H2Osystem, ring expansion of
these thiolketals with enolizable hydrogen was not detected. These
methods provide advantages, such as chemoselectivity, easy preparation,
simple work up, excellent yields, and the ability to recycle the
catalyst, which makes this method more useful compared to other
known methodologies.
