PTC,

It is liquid-liquid reactions involving phase transfer catalysts which generally benefit from the use of ultrasound. Sonication produces homogenisation - i. e. very fine emulsions - which greatly increase the reactive interfacial area and allows faster reaction at lower temperatures. Davidson has reported an example of this with the ultrasonically enhanced saponification of wool waxes by aqueous sodium hydroxide using tetra n-heptyl ammonium bromide as a PTC [124]. 

PTC 124 was identified after solid-phase combinatorial optimization of a screening hit from an 800 000 compound screening library [39]. Because the compound induces ribosomal read-through of premature termination codons... 

Allcock HR, Cameron CG, Smith DE (1995) PTC Int Appl WO, 95 28,150, Chem Abstr 124,89025m (1996), assigned to The Penn State Research Foundation... 

In contrast to the normal and reversed PTC methodologies, in which the chemical transformation takes place in the organic phase, it is reasonable to expect that PTC reactions can also be performed by transferring the organic reactants from the organic phase into the aqueous phase for reaction with a second reactant. Such a complementary methodology is named as inverse phase transfer catalysis (IPTC) by Mathias and Vaidya [124]. Recently, the application of IPTC in organic synthesis has been reviewed by Li et al. [150]. 

Very high enantioselectivities in the PTC Michael addition of 1,3-dicarbonyl compounds to enones have been achieved by Maruoka et al. [189,233] As shown in Scheme 2.86, just a 2 mol% of the binaphthyl-derived phase-transfer catalyst 124b [Scheme 2.70, 124, Ar=3,5-((CFj)jC H3)] in the presence of 10 mol% of solid KjC03, is able to achieved a highly efQdent and enantioselective addition of 2-(9-fluorenoxycarbonyl)cyclopentanone to methyl vinyl ketone [189]. 

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