Ring-rearrangement metathesis, examples

Cross metathesis (CM) reactions can also be used as the key step in a piperidine synthesis (Scheme 40) <2004TL1167> or in sequence with ring-rearrangement metathesis, for example, in the synthesis of (—)-lasubine (Scheme 41) <2004T9629>. 

Scheme 21 Representative examples of ring-rearrangement metathesis (RRM).

Fukuyama and coworkers [48] have also utilized an olefin additive in the optimization of a crucial ring-rearrangement metathesis sequence to form the key 5,6-ring system in the synthesis of (-)-isoschizogamine (Scheme 12.27). The tandem metathesis reaction of the norbornene 87 was difficult due to the substitution pattern of norbornene skeleton, which restricted the approach of the Ru catalyst. For example, the treatment of norbornene 87 with the second-generation Hoveyda - Grubbs catalyst 4 at reflux in benzene provided lactone 89 in only 24% isolated yield. To optimize this reaction, the use ofthe modified Hoveyda-Grubbs catalyst 88 [49] and the addition of 20 equiv of 1,6-heptadiene as an additive were quired. The desired lactone 89 was then obtained in 73% yield. 

The reactions of dienes and other polyenes can be broadly classified as either addition reactions, coupling (or substitution reactions) or rearrangements (including metathesis reactions). This chapter will present recent examples from the literature of synthetic transformations involving polyenes. Cycloaddition and ring closing metathesis reactions appeared in volume one of this series and therefore will not be covered in this chapter. Citations for more detailed descriptions of the individual reactions discussed in this chapter and for more comprehensive reviews appear in the text. 

These reactions involve metallate rearrangements , migratory insertion and transition metal-catalysed vinylic substitution reactions. They also perform well in applications in natural product synthesis . Many useful synthetic possibilities arise from application of ring-closing olefin metathesis (RCM) to unsaturated homoaldol products and their derivatives by means of the Grubbs catalyst 3942 4-286 Equation 105 presents some examples. ... 

We look at these reactions in detail in Sections 11.3 and 6.6, respectively. For the moment we need only note that the p-C—H of these cyclic dialkyls is held away from the metal and so is not available for p elimination. The P C—C bond is held close to the metal, however, and so these rearrangements are really p eliminations involving a C—C, rather than a C—H, bond. The reaction of Eq. 3.21 is of particular significance because it is the key step of an important catalytic reaction, alkene metathesis, which converts propene to butene and ethylene (Chapter 11). The anion of [Li(tmeda)]2[(CH2)4-Pt(CH2)4] contains two tetramethylene rings bound to square planar Pt(II) and is thermally rather stable. Cyclic diaryls are rare an interesting and very stable example is shown below ... 

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