Analysis antithetic

One of the most basic techniques is to work backwards, the final product or target molecule being the ultimate goal. This target is examined to find any or all compounds which can be transformed into it in a single chemical step. Each of these precursors may then be similarly analyzed until satisfactory starting materials are obtained. This method of analysis is called retrosynthetic (or, equivalently, antithetic). 

A structural modification that is being performed in the retrosynthetic direction is called a transform and is graphically depicted as a double arrow. 

When applied in its most general form, retro-synthetic analysis could be applied to every precursor of the target molecule and then, in turn, to each of the new structures. The graphical representation of such an analysis is called a synthesis tree. (A complex example is shown below). It is worthwhile to note that structures tend to be less complex the further away they are from the target molecule and no constraints are placed on the choice of reactions. 

The starting materials are the last to be generated, thereby maintaining flexibility in the choice of route until the end of the analysis. 

ACS Symposium Series Ameriean Chemieal Soeiety Washington, DC, 1977. 

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Since (A) does not contain any other functional group in addition to the formyl group, one may predict that suitable reaction conditions could be found for all conversions into (A). Many other alternative target molecules can, of course, be formulated. The reduction of (H), for example, may require introduction of a protecting group, e.g. acetal formation. The industrial synthesis of (A) is based upon the oxidation of (E) since 3-methylbutanol (isoamyl alcohol) is a cheap distillation product from alcoholic fermentation ( fusel oils ). The second step of our simple antithetic analysis — systematic disconnection — will now be exemplified with all target molecules of the scheme above. For the sake of brevity we shall omit the syn-thons and indicate only the reagents and reaction conditions. 

We close the section on open-chain molecules with an example of a trifunctional target molecule. This does not include any fundamentally new problem. In antithetic analysis one simply chooses an appropriate difunctional starting material, which may be further disconnected into monofunctional starting materials. 

From the above discussion it should be obvious that antithetical analysis of difunctional molecules simply is a reversal of the synthesis scheme already described in chapter 1. 

Antithetic Analysis. (Synonymous with Retrosynthetic Analysis) A problem-solving technique for transforming the structure of a synthetic target molecule to a sequence of progressively simpler structures along a pathway which ultimately leads to simple or commercially available starting materials for a chemical synthesis. 

H "The overall plan was derived using the strategy of antithetic analysis and depended on the tactic of generating the macrocydic unit by lactonization. Another major strategic element in the present approach is the use of sixmembered cyclic intermediates to establish and confirm the stereorelationships required for the C(l) to C(9) segment." (Corey, 1978) [6] ... 

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