Geranyl derivatives

Figure 16.1-26. Application of the pH-dependent oxidation of geranyl derivatives to the synthesis of some natural products.

In the rearrangement of allyl-substituted oxazoles, derived from Ar-benzoyl protected x-amino acids by cyclization with phosgene524, 525 or with triphenylphosphane/carbon tetrachloride502 as dehydrating agent, high selectivity is more of an exception, e.g., for the geranyl derivative 10524. 

Phosphorus and sulfur containing geranyl-geranyl derivatives... 

TABLE 1. The Effect of Leaving Groups in the Pd-Catalyzed Reaction of Geranyl Derivatives with (E)-2-Methyl-l-hexenyl-dimethylalane (at 22 °C)... 

Pd(PPh2) catalyses the reaction of various geranyl derivatives (e.g., -Cl, -OAc, -OAlMeg, -OPO(OEt)2, -OSiMOg, and -0SiMe2Bu ) with the alkenylalane (200) to give the triene (201). 

B.ii.b. AUylic Electrophiles. Pd-catalyzed allylation can take place with a wide variety of allylic electrophiles. A systematic study of the scope with respect to the leaving group in the reaction of alkenylalanes with geranyl derivatives summarized in Table 1 has indicated that not only Cl and OAc, but also other oxy groups such as OAIMe2, OPO(OEt)2, and even OSiRs including OSiMcs and OSiMcaBu-I participate in the reaction at room temperature. ... 

Since both neryl pyrophosphate and linaloyl pyrophosphate (or some equivalent species) (34) have been seriously considered as likely acyclic precursors to this family of monoterpenes, it is appropriate to examine first the cationic reactions of these two compounds. A great many investigations have shown that, while geranyl derivatives undergo substitution reactions in a fashion typical of an allylic substrate, both neryl and, less efficiently, linaloyl derivatives lead to cyclic products such as a-terpineol, and its dehydrated relatives limonene, and terpinolene... 

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