Polycyclic Substrates

The following illustrate the variety of hydroxylations of structurally diverse polycyclic substrates ... 

Fig. 31 Predicted versus observed mutagenic activities (log TA100) for (a) mutagens in Table 17 (entries 1-43 (squares), 48-54 (circles)) and (b) other polycyclic substrates (entries 55-58, triangles, diamonds) based upon QSAR (4).

The allene generating reaction has also been applied to more complex bi- and polycyclic substrates. Two examples from the recent literature suffice to illustrate... 

When a mineral or Lewis acid replaces the carboxylic component in the Passerini reaction, the final products are usually a-hydroxyamides. Also in this case, when chiral carbonyl compounds or isocyanides are employed, the asymmetric induction is, with very few exceptions, scarce [18, 19]. For example, the pyridinium trifluoroacetate-mediated reaction of racemic cyclic ketone 14 with t-butyl isocyanide is reported to afford a single isomer [19] (Scheme 1.7). This example, together with those reported in Schemes 1.3 and 1.4, suggests that high induction may be obtained only by using rigid cyclic or polycyclic substrates. 

Derivatives of polycyclic hydrocarbons have played a central role in the development of physical organic chemistry 29°). Polycyclic substrates have been found to be ideal models for numerous quantitative investigatious since their conformations are generally rigid and fixed and since they provide a large variation in structural types. Recent, comprehensive reviews of bridgehead reactivity are available 187> 291f... 

With some polycyclic substrates, a tandem ring expansion and ring contraction can take place under conditions of oxidative rearrangement. The 11-oxolanostanyl acetate (48 equation 46) undergoes such a reaction, in which ring c is contracted and ring d is expand and aromatized. The yield is poor though, and such a transformation would seem to have limited synthetic potential. 

Vogel observed deketalization, regioselective ring opening and aromatization in one step in the reaction of 218 with TMSOTf, Eq. 131 [188]. This step was part of a sequence for the asymmetric synthesis of anthracydinones from fused polycyclic substrates containing the [2.2.1] oxabicyclic nucleus. 

This methodology has been used to showcase new methodology for catalyst and reaction optimization employing nonaqueous capillary-array electrophoresis coupled with microreaction technology [ 116]. By tethering the alkyne to the nitrogen of the indole ring, one can readily prepare polycyclic substrates (Eq.57) [117,118]. 

The oxidatively assisted nucleophilic substitution of iodine with perchlorate anion in primary and secondary substrates proceeds according to an 5n2 mechanism as indicated by the stereochemistry of this reaction in the polycyclic substrates 640 leading to products 641 with inverted configuration (Scheme 3.251) [668]. 

The comparative analysis of the development of the Favorskii rearrangement mechanism in cyclohexane and constrained polycyclic substrates allows... 

Eschenmoser s salt. If ornithine or lysine derivatives are used instead as trapping agents, even more complex polycyclic substrates containing eight- or nine-membered rings could be obtained (13JA9608). 

C-glycosides [290], Moreover, polycyclic substrates permitted the reaction to proceed with an excellent diastereoselectivity (Scheme 6.33) [291]. 

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