Attachment of Carbonyl Compounds as Acetals

Support-bound alcohols and thiols can be used to immobilize aldehydes and ketones as acetals. Mixed acetals of carbonyl compounds with support-bound alcohols can be prepared by transacetalization of a symmetric acetal under acidic conditions [719]. The formation of mixed acetals on solid phase is, however, not always easy to perform and control, and so prior preparation of a mixed acetal in solution followed by loading onto a support is often the preferred protocol [626,637]. Carbohydrates can be linked to resin-bound alcohols or thiols as glycosides (Table 3.40). 

Resin-bound diols, amino alcohols, and dithiols, which reversibly form cyclic acetals with aldehydes and ketones, have been successfully used as linkers for carbonyl compounds (Entries 5-11, Table 3.40). Acetal formation on insoluble supports can be achieved by azeotropic removal of water (C6H6, TsOH, reflux [720]), whereas dithio-acetals can be prepared by acid-catalysis alone (BF3 OEt2 or TMSC1 CHCI3,0 °C, 2 h [721]). /V-Acylaminals such as R-CFI(OMe)NFI-CO-Pol have been prepared by treatment of resin-bound amides H2NCO-Pol with aldehydes in the presence of HC(OMe)3 and TFA [722], 

Entry Loaded resin Cleavage conditions Product, yield (purity) Ref. 

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