Steps in Planning a Synthesis

In planning an organic synthesis, the following key interrelated factors may be involved  

Construction of the carbon skeleton Functional group interconversions 

Reactions that result in formation of new carbon-carbon bonds are of paramount 

Below are summarized some important guidelines for choosing disconnections of bonds. Thus, the initial stage of the retrosynthetic analysis key fragments are recognized, which then can be recombined in the forward synthetic step in an efficient way.  

Disconnection via path a leads to synthons whose SEs can be reconnected by a nucleophilic attack of phenoxide on the propyl bromide to furnish the desired TM. On the other hand, disconnection via path b would require either attack of n-PrO on bromobenzene to reconstruct the TM, a reaction that is not feasible, or displacement of a benzenediazonium salt by n-PrO M .  

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In this section, we consider several syntheses of six illustrative compounds. We examine the retrosynthetic plans and discuss crucial bond-forming steps and the means of stereochemical control. In this discussion, we have the benefit of hindsight in being able to look at successfully completed syntheses. This retrospective analysis can serve to illustrate the issues that arise in planning a synthesis and provide examples of solutions that have been developed. The individual syntheses also provide many examples of the synthetic transformations presented in the previous chapters and of the use of protective groups in the synthesis of complex molecules. The syntheses shown... 

The incorporation of functionality into an ion slated for use in formulation of an ionic liquid is a usually a multi-step process. Consequently, a number of issues must be considered in planning the synthesis of the ion. The first of these is the choice of the cationic core. The core of a TSIL cation may be as simple as a single... 

Attack this problem by first planning a synthesis of 4-methyl-2-pentyne from any starting material in a single step. Two different alkyne alkylations suggest themselves ... 

We have now illustrated, in a few typical examples, some of the actors that go into the planning and execution of a contemporary organic synthesis. One could well ask at this point, Is it possible to formulate a set of general rules that may direct the composition of an optimal synthetic plan Let us state up front that no such summary of rigorous rules exists that define a sequence of steps to be taken in the solution of some given synthetic task. It is possible, however, to list several general recommendations which, while not universal, are unquestionably useful in the planning a synthesis. 

Some basic rules of planning a synthesis are choose reactions with high conversion choose reactions with high selectivity aim for the fewest number of steps possible try to run as many steps in parallel as possible and avoid low yielding or unreliable steps late in the synthesis. 

The core of planning a synthesis is to select the individual bonds of a bond-set and the sequence of bond-forming steps in such a manner that in the end an efficient synthesis of the target structure can be realized. Several (quite different) guidelines help in this process. A survey of a multitude of published syntheses reveals that bonds in a bond-set are marked according to ... 

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