10. Patented Literature 2616 10.1. Esterification 2616 10.2. Ether Formation 2619 10.2.1. Etherification without Cyclization 2619 10.2.2. Etherification with Cyclization 2624 10.3. N-Alkylation 2625 10.4. Other Reactions 2627 11. Summary and Outlook 2628 12. Note Added in Proof 2628 13. Abbreviations Used in This Review 2629 14. Acknowledgments 2629 15. Supporting Information Available 2630 16. References 2630

Mitsunobu and Related Reactions: Advances and Applications

Synthesis, stereochemistry, structural classification, and chemical reactivity of natural pterocarpans.

Pyrans and their Benzo Derivatives - Synthesis

Publisher Summary This chapter reviews papers that were published in 2006 on the reactions and syntheses of furans, benzofurans, and their derivatives. Like 2005, many new naturally occurring molecules containing tetrahydrofuran and dihydrofuran rings were identified in 2006. Several examples reported in 2006 demonstrate that 2-substituted furans underwent spirocyclization at the 2-position. The reaction of a furan tethered at the 2-position to an iminium ion gave a spiro-2,5-dihydrofuran derivative as the sole diastereoisomer. This spirocyclization that proceeded irrespective of the length of the carbon linker was employed to construct the ABC tricyclic core of manzamine A. Spirocyclization was also the reaction pathway under radical conditions if furan was tethered to a radical precursor at the 2-position. When furans were tethered to silyl enol ethers at the 2-position, spiroannulation also occurred at the 2-position under electrochemical conditions. Furan that was loaded on a soluble dendritic polyglycerol support could be efficiently oxidized electrochemically to a 2,5-dihydro-2,5-dimethoxyfuran, which served as an intermediate in the synthesis of a pyrrole library.

Chapter 5.3 Five-membered ring systems: Furans and benzofurans

A simple approach to highly functionalized benzo[b]furans from phenols and aryl iodides via aryl propargyl ethers

The preparation of 4-(o-bromophenoxy)-2H-1-benzopyrans and their conversion into the pterocarpan skeleton via radical cylisation are reported.

Radical cyclisation of 4-(o-bromophenoxy)-2H-1-benzopyrans; an efficient synthesis of pterocarpans

Synthesis of Pterocarpans by Means of a “Disfavored” 5-endo-trig Radical Cyclization Reaction

A simple route to chroman-4-ones from γ-bromopropynyl aryl ethers (1) using mercury(II) trifluoroacetate as a catalyst is described.

A novel and convenient mercury(II) mediated synthesis of chroman-4-ones

A Novel and Convenient Mercury(II) Mediated Synthesis of Chroman-4-ones.

A successful synthesis of pterocarpans 1, based on a "disfavored" 5-endo-trig radical cyclization reaction, has been accomplished. The radical precursor 4-(2'-bromoaryloxy)-2H-chromene 8 was synthesized in six steps, starting from aryl propynyl ether 2. On treatment with tributyltin hydride in refluxing benzene, aryl enol ether 8 underwent radical cyclization to furnish the pterocarpan 1. A deuterium label study was performed to prove the occurrence of 5-endo-trig radical cyclization. This methodology was extended further to synthesize a class of hitherto unknown pterocarpans 13. A novel and stereoselective route towards the synthesis of aryl ethers of bromohydrins by means of the Mitsunobu reaction is also described.

K. K. Balasubramanian

Papers

Radical cyclisation of 4-(o-bromophenoxy)-2H-1-benzopyrans; an efficient synthesis of pterocarpans

Synthesis of Pterocarpans by Means of a “Disfavored” 5-endo-trig Radical Cyclization Reaction

A novel and convenient mercury(II) mediated synthesis of chroman-4-ones

A Novel and Convenient Mercury(II) Mediated Synthesis of Chroman-4-ones.

Synthesis of Pterocarpans by Means of a “Disfavored” 5-endo-trig Radical Cyclization Reaction.