Cyclisations, solid acid catalysed

As the kTw value for water at 250 °C is three orders of magnitude higher than under ambient temperatures, this makes HTW and SCW attractive solvents for performing acid- and base-catalysed reactions and reduces the need to add external acids or bases to the solution. Furthermore, cooling serves to neutralise the solution, which provides a relatively straightforward approach to reaction quenching. This is an attractive feature for industry, which often relies upon the addition of mineral acids or solid-state acids to catalyse reactions. The circumvention of the need for external acid catalysts therefore reduces the quantity of hazardous byproducts that require neutralisation. Examples of acid-catalysed reactions in HTW and SCW include acylations, condensations, cyclisations, eliminations and hydrolyses , which have been recently reviewed elsewhere. ... 

Solid-phase combinatorial synthesis of AT-acyl-L-HSL has also been reported. The procedure entails the DIC/HOBt catalysed acylation of methionine functionalised resin with a carboxylic acid followed by BrCN-mediated cyclisation process to produce HSL libraries with retention of stereochemistry (Scheme 5) [55]. 

---