Retrosynthetic changes

Retrosynthetic. The direction of chemical change opposite to that of laboratory execution of a reaction (synthetic direction) the reverse-synthetic sense. 

It is not necessary to emphasise here that the inadequate use of the "control" (see instruction manual. Appendix B-2) for changing the order of disconnections may "spoil" the logic of a retrosynthetic analysis. Thus, giving the highest priority to "FINALS", for example, may destroy all the existing bifunctional relationships which would offer the best solutions. 

Creation of the synthon from the retron. The user carries out on the retron structure the corresponding changes to elaborate the synthon. For example, if we want to convert, in retrosynthetic direction, an alcohol into a carbonyl (the equivalent to a reduction reaction), an alcohol group has to exist in the retron, and the user must indicate "the formation (retrosynthetic) of a carbon-oxygen bond". 

In a retrosynthetic sense, formal hydrolysis of the carbon-nitrogen bond of 1.21 reveals enol 1.22 which would exist as the more stable ketone tautomer 1.23. Note that in the hydrolytic disconnection step the carbon becomes attached to a hydroxy group and the nitrogen to a hydrogen atom - there is no change in the oxidation levels of carbon or nitrogen. 

Remember that it helps to use retrosynthetic analysis in synthesis problems. This means working backward to simpler and simpler compounds until an available compound is reached. These problems offer an additional clue in that the starting material is specified. In such cases it is often useful to identify which carbons in the target come from the carbons of the starting material. It is usually advisable to change these carbons as little as possible. It is also useful to identify which carbon-carbon bonds must be formed in the synthesis and how any functional groups need to be modified. In some cases the entire path will be apparent after this examination. In others it will be neces-... 

Retrosynthetic analysis involves the disassembly of a TM into available starting materials by sequential disconnections and functional group interconversions. Structural changes in the retrosynthetic direction should lead to substrates that are more readily available than the TM. Synthons are fragments resulting from disconnection of carbon-carbon bonds of the TM. The actual substrates used for the forward synthesis are the synthetic equivalents (SE). Also, reagents derived from inverting the polarity (IP) of synthons may serve as SEs. 

The sections below provide specific examples of different routes to polyacetylenes. They are organized from a retrosynthetic standpoint. Most address one or both of the themes mentioned above the effect of changing conjugation length, and the need to circumvent the intractability of (CH) . 

A simple retrosynthetic analysis reveals that the neonicotinoids consist of a chloromethyl-substituted heterocycle and in most cases a nitroguanidine part. For discovery research as for industrial synthesis, the accessibility to these budding blocks is of considerable importcmce. Prior to the emergence of neonicotinoids, heterocycles of this structural type had not drawn particular attention, what has clearly changed ever since. [143,144]... 

Second, we need to determine whether there is a change in the identity or location of the functional group. In this case, the functional group has changed both its identity and its location. The functional group in the product is an aldehyde moiety. As seen in Section 10.7, an aldehyde can be made via hydroboration-oxidation of an alkyne. As shown with the retrosynthetic arrow, a terminal alkyne can be converted into an aldehyde. 

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