Tuning of reactivity

Example 6. High Solids, Two-Component, Clear, Aliphatic, Polyurea Coating. This example of an aliphatic, 100% urea coating utilizes polyaspartic esters as reactive diluents (see Section 4.2.3). These compounds allow fine tuning of reactivity and physical properties and eliminate the need for viscosity-reducing solvents. 

This unique phenomenon provides a powerful strategy in the molecular design of chiral catalysts that is, the requisite chirality can be served by the simple binaphthyl moiety, while an additional structural requirement for fine-tuning of reactivity and selectivity can be fulfilled by an easily modifiable achiral biphenyl structure. This certainly obviates the use of two chiral units, and should be appreciated in the synthesis of a variety of chiral catalysts with different steric and/or electronic properties. Actually, quaternary ammonium bromide possessing a sterically demanding substituent such as (S)-12b can be easily prepared, and benzylation with (S)-12b as catalyst gave 9 in 95% yield with 92% ee. Further, theenantioselectivity was enhanced to 95% ee with (S)-12c as a catalyst [12]. 

Pietruszka, J. Modern glycosidation methods tuning of reactivity. Carbohydrates 2003, 195-218. 

Qian, C. Zhu, D. Studies on organolanthanide complexes. Part 55. Synthesis of fiiran-bridged bis(cyclopentadienyl)lanthanide and yttrium chlorides, and hgand and metal tuning of reactivity of organolanthanide hydrides (in situ). J. Chem. Soc., Dalton Trans. 1994, 1599-1603. 

NHC might affect reactivitjr, as well as allowing for the tuning of reactivity via structural modifications. 

Chapter 6 Modem Glycosidation Methods Tuning of Reactivity,... 

Suginome, M. and Fu, G.C. (2000) First synthesis and resolution of a planar-chiral tetrahydroindolyl complex of iron electronic tuning of reactivity and enantioselective nucleophilic catalysis. Chirality, 12, 318-324. 

Hence, the amino acids with different side chains can be considered for fine-tuning of reactivity, especially for unstable enediyne systems, due to the correlation between bulkiness and onset temperature of Bergman cyclization. Reactivity and participation of amino groups in reactions following initial Bergman cyclization is to be taken into account when dealing with enediyne—peptide conjugates. 

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