Spirocyclic C-arylglycosides were synthesized from the appropriately protected delta-gluconolactones. Addition of lithium acetylide followed by glycosylation with 3-(trimethylsilyl)propargyl alcohol converted the delta-gluconolactones into silylated diynes. After desilylation, subsequent ruthenium-catalyzed cycloaddition of the resultant diynes with alkynes or chloroacetonitrile gave spirocyclic C-arylglycosides in good yields and selectivity. This strategy was also extended to the synthesis of spirocyclic C-arylribosides from the known gamma-ribonolactone derivative. Moreover, silver-catalyzed iodination of the sugar diynes followed by ruthenium-catalyzed cycloaddition with acetylene delivered spirocyclic C-iodophenylglycosides and -ribosides, which were subjected to palladium-catalyzed C-C bond-forming reactions and copper-catalyzed coupling with nitrogen heterocycles to lead to various derivatives.
Biologically interesting 2,5-dihydrofuran-fused quinones were synthesized via the ruthenium-catalyzed [2 + 2 + 2] cycloaddition of an ether-tethered diiododiyne with alkynes, copper-catalyzed Ullmann coupling of the resultant fused p-diiodobenzenes with methanol or allyl alcohol, and subsequent oxidation of phenol derivatives. The double Claisen rearrangement of the bis(allyl) ether product furnished a diallylhydroquinone derivative, which underwent iron-catalyzed oxidation, ring-closing metathesis, and dehydrogenation to deliver 1,3-dihydronaphtho[2,3-c]furan-4,9-dione.
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