Trialkylphosphonium oxoborates as C(sp3)-H oxyanion holes and their application in catalytic chemoselective acetalization

The use of trialkylphosphonium oxoborates (TOB) as catalysts is reported. The site-isolated borate counter anion in a TOB catalyst increases the availability of C(sp(3))-H to interact with electron donor substrates. The catalytic protocol is applicable to a wide range of substrates in the acetalization reaction and provides excellent chemoselectivity in the acetalization over thioacetalization in the presence of alcohols and thiols, which is otherwise hard to achieve using typical acid catalysts. Experimental and computational studies revealed that the TOB catalysts have multiple preorganized C(sp(3))-Hs that serve as a mimic of oxyanion holes, which can stabilize the oxyanion intermediates via multiple C(sp(3))-H non-classical hydrogen bond interactions.

Automated summary

The use of TOB catalysts increases the interaction between C(sp(3))-H and substrates, providing excellent chemoselectivity in acetalization reactions, particularly in the presence of alcohols and thiols. Experimental and computational studies have shown that TOB catalysts have preorganized C(sp(3))-H structures that stabilize oxyanion intermediates.