Cleavage reactions, solid support catalysts

Historically, the first cracking catalyst used was aluminum trichloride. With the development of heterogeneous solids and supported catalysts, the use of AICI3 was soon superseded, since its activity was mainly due to the ability to bring about acid-catalyzed cleavage reactions. 

The first step consisted of the Mitsunobu etherification of an allyl alcohol with the resorcinol monoester, which afforded 102. Cleavage of the benzoyl protecting group released the phenol, which was then attached to the solid support. One-step cleavage of the THP group and bromination was achieved with PPhs/C Br4 to furnish 103. Nucleophilic substitution of the bromide with benzylamine was followed by acylation of the secondary amine wtith N-Boc-allylglycine 104, which resulted in the precursor 105, ready for the metathesis reaction this was performed with catalyst 101 to yield the final product 106. Either 1-octene or ethene was employed to generate 101. 

An early report by Konig deals with rapid parallel Suzuki reactions in water with phase-transfer catalysts. The solid support used in these reactions was PEG, and a variety of aryl palladium precursors were evaluated aryl halides as well as aryl tri-flates and nonaflates (Scheme 15.8). The inclusion of PEG is appealing, because it not only helps to solubilize the reagents but is also suggested to stabilize the palladium catalyst in the absence of phosphine ligands. Both the polymers and the esters were reported to withstand 10 min of 900 W multimode MW irradiation whereas the thermal conditions induced substantial ester cleavage (up to 45%). Nonaflates were found to be associated with lower yields and diminished product purity [32]. 

Mono-O-allyl derivatives of o-fructose have been prepared in order to test the specificity of the fructose transporter GLUT5. Tris(triphenylphosphine)ruthe-nium(II) dichloride is an excellent catalyst for the isomerization of allyl to prop-l-enyl ethers in a de-O-allylation procedure. The catalyst avoids the problem of reduction of the alkene as a side reaction. " Another method uses Pd(0)-catalysed allyl transfer to p-toluenesulfinic acid for the cleavage of allyl ethers on a solid support."... 

---