Retrosynthetic synthesis strategy

A retrosynthetic synthesis of (—)antirhine (Fig. 11) was performed through the monoacetate (1) and lactone (2) which was condensed with tryptamine. Product 3 was then finally converted, through a number of intermediates, to the tetracyclic (—)-antirhine, resulting in a remarkable overall yield of 13% (starting from the monoacetate 1), together with the 3-epimer (+)-antirhine at a yield of 6%. This strategy allowed the chemo-enzymatic synthesis of both (—) - and (+)-antirhines [82]. 

The block synthesis strategy is demonstrated here by the synthesis of the dimeric-Lewis octasaccharide (29) described by Schmidt and coworkers [8,9]. As shown in the retrosynthetic analysis (Scheme 5.5), the octasaccharide (29) should be accessible from the tri- (30) and disaccharide (31) units, represented by the blocks 32 and 33. The trisaccharide block can be disconnected from the L-fucosyl (34) and D-galactosyl (35) imidates and the 2-azido-2-deoxy-o-glucose derivative (36). 

For an introduction to retrosynthetic analysis see Corey, E. J. Cheng, X-M. The Logic of Chemical Synthesis , John Wiley and Sons, 1989 (pages 5-16). See also Wyatt, R Warren, S. Organic Synthesis — Strategy and Control John Wiley and Sons, 2007. 

CHAllEHGtl Propose an efficient synthesis of the cyclohex-enol below, beginning exclusively with acychc starting materials and employing sound retrosynthetic analysis strategy. [Hint A Diels-Alder reaction may be useful, but take note of structural features in dienes and dienophiles that permit Diels-Alder reactions to work well (Section 14-8).]... 

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.). 

These strategies guide the retrosynthetic conversion of 272 to 278 and the further conversion of 278 via 279 to 282. The r-butyl substituent actuates the clearability of the stereocenters in 279. Further retrosynthetic simplification as dictated by basic FG-, stereochemical and topological strategies then leads from 280 to 281 and to 282, a previously described substance. The successful synthesis followed closely the above outlined retrosynthetic scheme. An enantioselective process was devised for the synthesis of 281 from 282 (see Section 10.12).67, 83... 

Despite the structural relationship between ginkgolide B and bilobalide, retrosynthetic analysis of the latter produced a totally different collection of sequences. A successful synthesis of bilobalide was implemented using a plan which depended on stereochemical and FG-based strategies. A process for enantioselective synthesis was based on an initial enantioselective Diels-Alder step in combination with a novel annulation method. 

The various name reactions that have appeared in the literature over the years make use of a common retrosynthetic strategy, namely, disconnection at the C-N bond. Depending on how and at what time in the synthesis these bonds are formed dictates how the synthetic approach is classified, thus the name applied to the procedure (see Figure 8.1.5). 

The retrosynthetic analysis described above outlines a triply convergent strategy towards the synthesis of zaragozic acid A (1). The most pleasing aspect of the retrosynthetic strategy is the rapid and enantioselective manner in which the two-dimensional molecule... 

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