Chapter 5.3 Five-membered ring systems: Furans and benzo derivatives

Publisher Summary This chapter provides information on five-membered ring systems, including furans and benzo derivatives. The chapter presents few examples of saricandin, glabrocoumarone A, benzo[b]furans, heyneanol A, mulberrofuran V, and others. Hydroxyfuranoeremophilanes are the main compounds of fleshly harvested rhizomes of Petasites hybridus . They easily and quantitatively rearrange in the presence of traces of acids to give an epimeric mixture of 8- H -eremophilanlactones. Novel mono-THF acetogenins (gigantransenin A, B, C) were isolated from Goniothalamus giganteus (Annonaceae). The synthesis of 2-pyridinyl-7 oxabicyclo[2.2.1]heptanes was accomplished via zinc chloride-mediated Diels–Alder reaction of furan with 2-vinylpyridines. The reaction of triflates (available via Diels–Alder reaction with furan or cyclopentadiene) with alkynylstannanes proceeds smoothly and with selectivity to afford good yields of bicyclic enediynes. Asymmetric Diels–Alder reactions of chiral sulfinyl acrylate derivatives with furans proceed under high pressure (1.2 GPa) conditions to give endo cycloadducts. Polysubstituted 3-thiofurans which are receiving a great interest as flavor and odor chemicals have been obtained by mono- ipso -substitution and ortho -metallation from 3,4-dibromofuran. Dihydrofuran is used in a new synthesis ofketones from acids via acyl hemiacetals.