Chemistry Reference
In-Depth Information
6
Polymer-Supported
Organosuperbases
Hiyoshizo Kotsuki
Faculty of Sciences, Kochi University, 2-5-1 Akebono-cho, Kochi 780-8520, Japan
6.1
Introduction
The immobilization of reagents or molecular catalysts in a polymeric form generally offers
several advantages in organic synthesis. These include: the ease of handling without the
need for special equipment or an inert atmosphere; the simplicity of separating the products
from complex reaction mixtures; the ease of recovering and recycling the reagents; and the
adaptability to continuous-flow synthetic processes. Accordingly, there have been a wide
variety of investigations to discover new efficient polymer-supported reagents, and great
achievements have beenmade in recent years, especially in the fields of pharmaceutical and
agrochemical research, and combinatorial chemistry [1-9].
In many cases, polymer-supported organic base reagents can be synthesized by the direct
attachment of a suitable strong base core on a polymeric backbone through a covalent bond
linkage. Typically, 1,1,3,3-tetramethylguanidine (TMG, pK
a
¼
23.7) [10], 1,5,7-triazabi-
cyclo[4.4.0]dec-5-ene (TBD, pK
a
¼
26.2) [10], 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU,
pK
a
¼
s phosphazene base, that is, 2-tert-butylimino-2-diethy-
lamino-1,3-dimethylperhydro-1,3,2-diazaphosphorine (BEMP, pK
a
¼
23.9) [10], the Schwesinger
27.6) [11], and the
s proazaphosphatrane base (PAPT, pK
a
¼
Ve r k a d e
32.9) [12], can be used as nonionic
strong bases (Figure 6.1).
The synthetic study of polymer-supported superbase reagents has grown from the
pioneering work from Tomoi
s laboratory [13-15]. There it was showed that N-alkylation
