10- Membered ring synthesis

Five-membered ring synthesis by formation of one bond 423... 

In this chapter we provide an overview of studies originating from the above work and directed at the design and development of three new metal-catalyzed cycloaddition reactions, namely the [5+2] cycloaddition of vinylcyclopropanes (VCPs) and rc-systems, the [6+2] cycloaddition of vinylcyclobutanones and re-systems, and the three-component, [5+2+1] cycloaddition of VCPs, rc-systems, and CO. These new reactions provide fundamentally new approaches to a range of problems in seven- and eight-membered ring synthesis. 

Scheme 13.5 Representative thermal cycloadditions for seven-membered ring synthesis.

Cycloadclition Approaches for Eight-Membered Ring Synthesis 291... 

Scheme 13.18 Representative examples of transition metal-mediated cycloadditions for eight-membered ring synthesis.

VCPs and 27r-components and the subsequent development of the first [5-i-2-i-l] three-component cycloaddition approach to eight-membered ring synthesis. 

The Baeyer-Villiger oxidation of cyclohexanone to form e-caprolactone (78) using peroxybenzoic acid, as indicated in equation (40), may be considered as a further type of intramolecular displacement reaction of value in seven-membered ring synthesis (49JA2571). 

Nickel catalysts for the syntheses of cyclic compounds were first successfully utilized by Reppe, who was able to prepare cyclooctatetraene from acetylene (65). This eight-membered ring synthesis, and also the preparation of cyclic products from strained olefins (e.g., bicycloheptene and norbornadiene) and acrylonitrile, have been adequately reviewed elsewhere (7) and will therefore not be considered further. A short account of the cyclization reactions of butadiene using nickel-containing catalysts has appeared previously in this series (/). The discovery of new synthetic possibilities and a deeper understanding of the mechanism of these reactions justify a more extensive treatment. 

The Norrish-Yang reaction, with the spin-center-shift extension, facilitates access to a variety of cyclic compounds. This will be discussed here, with examples of the synthesis of three- to six-membered rings synthesis of macro- and bicydic compounds and the photochemistry of imides will not be covered. The examples especially demonstrate the capabilities of the reaction with regard to stereoselectivity. 

Enolate D of Figure 13.73 undergoes an aldol condensation with the C=0 double bond. The enone A is the condensation product. This reaction represents a six-membered ring synthesis even though it is not a six-ring annulation. 

From five-membered rings Synthesis of pyrene derivatives from five-membered ring precursors by ring enlargement [13]. 

Trifluoromethyl-substituted nitrones have been prepared [78JFC-(12)153 88JFC(39)39, 88MI2 89JHC381] and used as building blocks for five-membered ring synthesis (Scheme 66). 

Five-membered Ring Synthesis by Formation of One Bond 334... 

---