Stereoselective preparation of enantiomerically pure annulated carbohydrates using ring-closing metathesis

Ring-closing metathesis has been applied to a series of glucose derivatives to produce cyclopentene derivatives 5a and 5b, cyclohexene derivatives 8 a nd 9, cycloheptene 12, and cyclooctene 14. Spirocyclic dihydrofurans 19, 26 a, and 26b, along with dihydropyran 22, were also produced. A range of fuse d oxepine derivatives 29a-c and one oxo-cyclononene 31 were also prepared. Cyclopentene 5b was subjected to a sequence of hydrogenation, NBS brominati on, and treatment with powdered zinc to furnish the ring-expanded product 3 5. No such ring expansion occurred when the cyclohexaannulated compound 8 w as treated with NBS followed by powdered zinc, leading to aldehyde 39. The spiro dihydrofuran derivative 19 was converted to the aldehyde 42 via the s ame reaction sequence used to fragment cyclopentene derivative 5b.