Chapter 6.4 (2006): Six-membered ring systems: with O and/or S atoms

Abstract

This chapter provides an overview of six-membered ring systems with O and/or S atoms. Methods for the construction of 1-oxadecalins, the synthesis of isochromans by the oxa-Pictet–Spengler cyclization, highly unsaturated pyrone polyketides, and photochromic naphthopyrans are discussed in the chapter. The cycloaddition reactions of transition metal-containing benzopyrylium species are reviewed in the chapter. This chapter reviews the heterocyclic synthesis by Pd-catalyzed oxidative addition, ring-closing metathesis (RCM) of heteroatom-substituted dienes, cascade reactions in total synthesis, and a discussion of stereochemical relays. In the chapter, the value of RCM in the construction of fused polycyclic ethers is discussed and approaches to ladder polyethers using epoxide-opening cascades and to those containing a 6/7 cis -fused system are presented. Enones have been converted into trans -fused pyranopyrans in four steps and an intramolecular acyloin condensation of a tetrahydropyran-2,3-diester is an integral part of another approach to this system. A 6/6/6/6 trans -fused tetracyclic ether bearing two guanidinium groups act as a receptor for aspartate pairs on an α-helical peptide.