USE OF SILICA-GELS AND MESOPOROUS MOLECULAR-SIEVES AS SUPPORTS FOR THE SOLID-PHASE CLAISEN REARRANGEMENT

A series of silica gels and mesoporous molecular sieves differing in b oth the range of particle size and mean pore size were derivatized wit h the oren-9-yl)-methoxyformamido]-2,4-dimethoxybenzyl]- phenoxyacetic acid linker and their loading capacities were measured. Loading capac ities ranging between 0.4-0.6 mmol Fmoc/g were achieved. Several of th ese silica based materials were derivatized with the hydroxymethyl ben zoic acid linker and used as supports for the solid phase Claisen rear rangement of a support bound phenyl allyl ether. Both the silica gel a nd mesoporous supports were heated at 225 degrees C for 3 h to effect the Claisen rearrangement. The results showed that, compared to the sa me reaction run homogeneously, the silica gel support achieved similar total product yields and ratios for two Claisen products. The mesopor ous supports were found to selectively produce one of the Claisen prod ucts over the other. Analysis shows that the molecules bound to the me soporous support are physically further separated from each other as c ompared to those bound to the silica gel support. A mechanism is prese nted which accounts for the selectivity of the mesoporous support in f orming one Claisen product over the other. The Claisen product was fur ther derivatized to the resulting phenyl ethyl ether through a solid p hase Mitsunobu reaction on the mesoporous support.