Synthetic Analysis and Planning

The general point is that synthetic analysis and planning should not be restricted to the specific functionalities that must appear in the target molecules. These groups can be incorporated as masked equivalents by methods that would not be possible for the functional group itself. 

The initial step in creating a synthetic plan should involve a retrosynthetic analysis. The structure of the molecule is dissected step-by-step along reasonable pathways to 

Corey and X.-M. Cheng, The Logic of Chemical Synthesis, John Wiley Sons, New York, 1989. 

The care with which a synthesis is analyzed and planned will have a great impact on its likelihood of success. A single flaw can cause failure. The investment of material and effort which is made when the synthesis is begun may be lost if the plan is faulty. Even with the best of planning, however, unexpected problems are frequently encountered. This circumstance again tests the ingenuity of the chemist to devise a modified plan which can expeditiously overcome the unanticipated obstacle. 

The degree of control of stereochemistry that is necessary during synthesis depends on the nature of the molecule and the objective of the synthesis. The issue becomes of 

The restrictions which apply to a synthesis will depend on the reason the synthesis is being conducted. A synthesis of a material to be prepared in substantial quantity may impose a limitation as to cost of starting materials. Syntheses for commercial production must meet such criteria as economic feasibility, acceptability of by-products, and safety. Synthesis of complex structures with several chiral centers must deal with the problem of stereoselectivity. If an enantiomerically pure material is to be synthesized, the means of controlling enantioselectivity must be considered. The development of a satisfactory plan is the intellectual challenge to the chemist. The task puts a premium on creativity and ingenuity. There is no single correct 

The care with which a synthesis is analyzed and planned will have a great impact on its likelihood of success. A single flaw can cause failure. The investment 

The degree of control of stereochemistry that is necessary depends on the nature of the molecule and the objective of the synthesis. The issue becomes of critical importance when the target molecule has several stereogenic centers, such as double bonds, ring junctions, and chiral centers. The number of possible stereoisomers is 2 , where n is the number of stereogenic centers. Failure to control stereochemistry of intermediates in the synthesis of a compound with several centers of stereochemistry will result in a mixture of stereoisomers, which will, at best, lead to a reduced yield of the desired product and may generate inseparable mixtures. 

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A third term which has become useful for the discussion of synthetic analysis and planning is synthon. This term refers to a structural unit which has the potential for some specific synthetic operation. Again using the example above, we are searching for a group which would serve as a nucleophilic acyl synthon that is, some structural entity that would correspond to the addition of a nucleophilic acyl equivalent to an electrophilic carbon-carbon double bond. 

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