Synthon concept

The concept of tecton can be better understood if contrasted with the concept of supramolecular synthon. Paraphrasing Corey s historic definition of synthon, Desiraju defined that a supramolecular synthon is a stmc-tural unit vvdthin a supermolecule that can be formed or assembled by known or conceivable synthetic operations involving intermolecular interactions. The supramolecular synthon concept is backwardly oriented (i.e., is useful in supramolecular retrosynthesis) and focuses on the part of a supermolecule that is formed or can be formed through an intermolecular interaction. The tecton concept is forwardly oriented (i.e., is useful in supramolecular synthesis) and focuses on a molecule that predictably gives supermolecules, thanks to its tailored structure and robust binding sites. 

The coimection between functionality at C-1 and reactivity at C-n is no longer present. Generally speaking, the synthon concept applies predominantly to distances between the functionality and reactive center of 1-3 skeletal atoms. Thus, the reach of a functional group in governing remote reactivity extends no further than the skeletal atom 3 . 

The development of the supramolecular synthon concept from pattern recognition considerably simplifies the analysis and design of complicated crystal structures [9], as topological features and useful empirical rules can be derived by critical examination of the wealth of crystallographic information documented in structural databases [10],... 

Over time, the term clathrate has become strongly intertwined with both Cram s host-guest concept and om increasing understanding of intermolecular forces within crystals. By 1962, Brown had established the fundamental topologies adopted by inclusion compounds, and a comprehensive classification of all host-guest stmctmal types was proposed in 1983. ° Introduction of the supramolecular synthon concept by Desiraju and more recent analysis of weak hydrogen bonds and other interactions have been of immeasurable value. 

Figure 5.1 Alkylfbrmyl subunit according to the synthon concept.

The supramolecular synthon concept combines the chemical elements of molecular recognition with the geometrical requirements of crystal packing. The seminal 1995 review paper of Desiraju introduced the formal Hterature definition of the supramolecular synthon, based on analogy with Corey s definition of synthons for covalent synthesis. The explicit link between eovalent synthesis and crystal engineering is stressed by this analogy, and co-erystal or... 

A convenient way to determine when to apply the acetoacetic ester or malonic ester approach to a synthetic problem is to incorporate the synthon concept into retrosynthetic analysis. A synthon is a structural unit in a molecule that is related to a synthetic operation. A CH2CO2H group is a synthon that alerts us to the possibility of preparing a target by a malonic ester synthesis. Likewise, a CH2C(0)CH3 group is a synthon that suggests an acetoacetic synthesis. 

One learns from these molecular complexes that equivalent synthons can lead to virtually identical crystal structures. Synthons in, V and VI are chemically and geometrically equivalent though they originate from different molecules, a nitrile, an N-oxide and a nitro compound. These three synthons are used in crystal design in almost the same way. So, different molecules may yield similar crystal structures if they are capable of forming equivalent synthons. This is a powerful concept because it establishes a many-to-one correspondence between molecular and crystal structures. 

Some comments on the concept of "transform " in the CHAOS program As we have said. Appendix B-3 shows all the "transforms" incorporated to CHAOS. The "retrons" are represented at the left side, and the result of their disconnection (the "synthons") appears at the right side. However, the user will... 

Based on the concepts of synthon 2 and the "additive Pummerer reaction" suggest a mechanism for the 1 —> 4 transformation. 

Bryostatin 7 (3) was the first member of the bryostatin family that was accessible by total synthesis. Its preparation was described by Masamune et al. already briefly after its isolation from Bugula neritina [8]. Their concept was based on a combination of the four synthons 4-7 (Figure 2) The (R,R)-2,5-dimethylborolanyl triflate mediated aldol reaction of aldehyde 4 with the enolate derived from ketone 5 leads after a sequence of deprotection steps, cycliza-... 

The concept of supramolecular synthon defines specific substructural units that contain the logical code for self-assembly by noncovalent bonds (consisting mainly of H-bonding interactions) [65]. A chiral counterpart of this concept is the supramolecular chiron [60,66]. It is defined as the minimal homo- or hetero-chiral molecular unit or ensemble capable of generating ordered superstructures by self-assembly through H-bonding or other noncovalent forces, and leading to... 

Wuest has demonstrated that the pyridone moiety also generates a hydrogen-bonded supramolecular synthon that is suitable for building extended arrays.67 Remarkably, methanetetra(6-phenylethynyl-2-pyridone) exhibits a diamondoid network, sevenfold interpenetration and cavities large enough to enclathrate butyric or valeric acid.27 Wuest introduced the concept of tectons to describe molecules that inherently possess the molecular structure and intermolecular recognition features to predictably self-assemble into crystalline networks. He followed this study with several other examples of diamondoid networks sustained by the pyridone moiety 27c d... 

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