Strategic reaction

Combined C-H activation/Cope rearrangement as a strategic reaction 178... 

The C-H insertion into alkanes described above is a surrogate of enolate alkylation (Figure 2). The two strategic reactions are complementary, because enolate alkylation is preferred at primary alkyl halides while the C-H activation tends to preferentially occur at tertiary C-H bonds. 

The combined C-H activation/Cope rearrangement generates a new C-H bond in a highly stereoselective manner and, therefore, has the potential to be a strategic reaction in synthesis. An example of this is the enantiose-lective synthesis of (+)-sertraline as shown in Scheme l.91 The C-H insertion step proceeded smoothly to form 17 with 99% ee. The conversion of 17 to (+)-sertraline could be readily achieved using conventional steps. 

C-H activation-Cope rearrangement, 10, 177 Claisen condensation equivalent, 10, 174 Claisen rearrangement equivalent, 10, 176 enolate alkylation equivalent, 10, 171 Mannich reaction equivalent, 10, 174 as strategic reaction, 10, 171 intermolecular C-H insertion, C-H activation-Cope rearrangement as strategic reaction, 10, 178... 

Cope rearrangement, combined carbene C—H activation—Cope overview, 10, 177 as strategic reaction, 10, 178... 

Select the strategic bond. This recommendation is especially important in those numerous cases in which the initial analysis does not identify an efficient strategic reaction and, hence, a sequential bond-by-bond dismantling of the structure becomes obligatory. The first bond in this sequence (the strategic bond) defines all subsequent steps in the retrosynthetic analysis. This approach was illustrated in the syntheses of quadrone (Section 3.2.5). 

A similar computer-assisted approach was also elaborated envisioning the choice of the Diels-Alder transform as a strategic reaction. The task of the program in this case is to suggest the retrosynthetic transformations of the target structure leading to the creation of the cyclohexene moiety amenable to the retro-Diels-Alder disconnection. The general coiu e of these pursuits is shown in Scheme 3.50. ... 

Figure 6 Synthetic planning make.s use of retrosynthetic transforms, and may work towards the use of a strategic reaction...

Experiment 5. Over and above longitudinal influences on the form of the limit cycle, cross-sectional influences can occur, such as an influence on the frequency of one nation s cycle by the business activities in other nations (locomotion theory). The resulting strategic reactions of this one nation s investors may further distort the limit cycle, so that a modified strongly non-sinusoi-dal reaction pattern emerges this then favours or disfavours a rush into certain types of investment see Figs. 5.8 a, b. 

Davies HML, Dai X, Long MS. Combined C—H activa-tion/Cope rearrangement as a strategic reaction in organic synthesis total synthesis of (—)-colombiasin A and (—)-elisapterosin B. J. Am. Chem. Soc. 2006 128(7) 2485-2490. 

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