科研之友
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摘要
To illustrate the general principle of asymmetric organocatalysis of chiral bicyclic guanidine, a density functional theory study was carried out to examine the catalytic mechanism, activation mode, origin of stereoselectivity of a [5,5]-bicyclic guanidine-catalyzed Michael addition of dimethyl malonate to 2-cyclopenten-1-one. Two types of bifunctional activation modes were examined: Bronsted acid and Bronsted-Lewis acid. The calculated enantioselectivity (ee), based on eight C-C bond forming transition states and their pre-transition state complexes, is in excellent accord with experimental result. The ternary pre-transition state complexes are stable species, which strongly influence the stereoselectivity. Similar to enzyme catalysis, the bicyclic guanidinium catalyst plays an essential recognition role in assembling the substrates together via hydrogen bonds, multiple C-H center dot center dot center dot O interactions (as oxyanion hole), donor-acceptor, and electrostatic interactions.
- 出版日期2014
