Reimer-Tiemann reaction regioselectivity

Redox equations, balancing, 265 Reduction of aromatic compounds, 200 Reductive amination, 404 Reductive hydroboration, 95 Reformatsky reaction, 321 Regioselective reactions, 97 Reimer-Tiemann reaction, 438 Resonance, 23 in benzene, 192 energy, 24 structures, 29 Resorcinol, 327, 432 Retroaldol condensation, 399 Ring activation, 2(fiff Robinson inaction, 398 Rosenmund reduction, 306... 

Ravichandran, R. P-Cyclodextrin mediated regioselective photo-Reimer-Tiemann reaction of phenols. J. Mol. Catal. A Chemical 1998,130, L205-L207. 

Since the Reimer-Tiemann reaction always yields a mixture of ortho- and para-substituted phenols whenever the two positions are unsubstituted (and sometimes even when the positions are substituted, see carboxy-substituted phenols), it is not surprising that attempts have been made to increase the regioselectivity. Earlier attempts (for details, see reviews) emphasized the nature of the cation, the solvent, or used phase-transfer catalysis. Recent studies have concentrated on the use of cyclodextrins as base-stable host compounds, permitting exclusive para substitution. Attaching the cyclodextrins to a solid support has also been attempted, a natural step in view of the high cost of the cyclodextrins and the need for cheap product i.e. p-hydroxybenzaldehyde). p-Hydroxybenzaldehyde has been prepared in 59-65% yield using P-cyclodextrin that has been immobilized with epichlorohydrin. TTie catalyst is easily recovered and can be reused without appreciable loss of activity. 

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