Retrosynthetic analysis,

When planning the synthesis of a compound using an organometalhc reagent, or indeed any s)mthesis, the best approach is to reason backward from the product. This method is called retrosynthetic analysis. Retrosynthetic analysis of 1-methylcyclohexanol suggests it can be prepared by the reaction of methylmagnesium bromide and cyclohexanone. 

To recognize the different levels of representation of biochemical reactions To understand metabolic reaction networks To know the principles of retrosynthetic analysis To understand the disconnection approach To become familiar with synthesis design systems... 

The aim of a retrosynthetic analysis is the transformation of a synthesis target into progressively simpler structures, following a pathway to commercially available starting materials. 

Since a reaction is considered during a retrosynthetic analysis in a direction opposite to its actual course, it is called a retro-reaction or transform (Figure 10.3-30). 

A siynthestis tree is the graphical representation of the result of a retrosynthetic analysis. The target compound (T) is set to the top of a tree that is turned upside down (Figure 10..3-3.3). 

Tran orm-based or long-range strategies The retrosynthetic analysis is directed toward the application of powerful synthesis transforms. Functional groups are introduced into the target compound in order to establish the retion of a certain goal transform (e.g., the transform for the Diels-Alder reaction, Robinson annulation, Birch reduction, halolactonization, etc.). 

The retrosynthetic analysis is performed in two steps in a first step, SYNGEN dissects the skeleton to find all fully convergent bondsets which utili2e starting material skeletons found in two successive levels of cuts. A bondset is a set of skeletal bonds that is cut during the retrosynthetic analysis or formed in any given synthesis. 

The Japanese program system AlPHOS is developed by Funatsu s group at Toyo-hashi Institute of Technology [40]. AlPHOS is an interactive system which performs the retrosynthetic analysis in a stepwise manner, determining at each step the synthesis precursors from the molecules of the preceding step. AlPHOS tries to combine the merits of a knowledge-based approach with those of a logic-centered approach. 

The retrosynthetic analysis of a target compound is a systematic approach in developing a synthesis plan starting with the target structure and working backward to available starting materials. 

The vitamin D3 metabolite la,25-dihydroxycholecalciferol is a lifesaving drug in treatment of defective bone formation due to renal failure. Retrosynthetic analysis (E.G. Baggjolint, 1982) revealed the obvious precursors shown below, a (2-cyclohexylideneethyl)diphenylphosphine oxide (A) and an octahydro-4f/-inden-4-one (B), to be connected in a Wittig-Homer reaction (cf. section 1.5). 

In the last fifteen years macrolides have been the major target molecules for complex stereoselective total syntheses. This choice has been made independently by R.B. Woodward and E.J. Corey in Harvard, and has been followed by many famous fellow Americans, e.g., G. Stork, K.C. Nicolaou, S. Masamune, C.H. Heathcock, and S.L. Schreiber, to name only a few. There is also no other class of compounds which is so suitable for retrosynthetic analysis and for the application of modem synthetic reactions, such as Sharpless epoxidation, Noyori hydrogenation, and stereoselective alkylation and aldol reactions. We have chosen a classical synthesis by E.J. Corey and two recent syntheses by A.R. Chamberlin and S.L. Schreiber as examples. 

On the basis of this retrosynthetic analysis design a synthesis of N methyl 4 phenylpipendine (compound A where R = CH3 R = C6H5) Present your answer as a series of equations show ing all necessary reagents and isolated intermediates... 

An overarching principle of great importance in retrosynthetic analysis is the concurrent use of as many of these independent strategies as possible. Such parallel application of several... 

The logical application of retrosynthetic analysis depends on the use of higher level strategies to guide the selection of effective transforms. Chapters 2-5 which follow describe the general strategies which speed the discovery of fruitful retrosynthetic pathways. In brief these strategies may be summarized as follows. 

Retrosynthetic Analysis by Computer Under T-Goal Guidance.23... 

The information obtained by this preliminary analysis can be used not only to set priorities for the various possible Diels-Alder disconnections, but also to pinpoint obstacles to transform application. Recognition of such obstacles can also serve to guide the search for specific retrosynthetic sequences or for the highest priority disconnections. At this point it is likely that... 

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