Strategy and Building Blocks

The propensity for Claisen-Schmidt condensation to afford bis-adducts [e.g., ( , )-2,6-dibenzylidenecyclohexanone from benzaldehyde and cyclohexanone] virtually exclusively, even in the presence of excess ketone (as mentioned in Section 6.2.3), was the cornerstone of our strategy for the preparation of symmetrical adducts (i.e., those with a two-fold axis through the C=O group as viewed in the plane of the page). Such condensations occur sequentially, as mono-condensed products tend to be more reactive than the parent cycloalkanones under the reaction conditions, making them transient intermediates prepared for further reaction. 

Each building block was designed to serve uniquely, as a terminal (male or female), as a rigid union (either male male or female female) or as a flexible connector (either male male or female female). Specifications and examples of each type of building block are presented for ease of explanation and illustrated 

With specific functionality built-in, each building block qualified as only one type of fitting. Vast combinatorial diversity, however, was made possible by an extensive range of building blocks that could satisfy each type. For example, any aryl, fused aryl or heteroaryl monoaldehyde could be utilized as a female terminal and any cyclic ketone with active a,a -methylene groups could constitute a rigid male-male union. 

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C. Selectivity and Regulation Design Strategies and Building Blocks... 

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