In the past two decades, alkene metathesis has risen in prominence to become a significant synthetic strategy for alkene formation. Many total syntheses of natural products have used this transformation. We review the use, from 2003 to 2015, of ring-closing alkene metathesis (RCM) for the generation of dihydrofurans or -pyrans in natural product synthesis. The strategies used to assemble the RC...

The title compound, C(21)H(24)O(11), crystallizes exclusively as the β-anomer. The substituent of the protected sugar at position C-3 is in the axial position, while all other groups are in equatorial positions. The pyran-oside ring adopts a stable chair conformation.

Photochromic pyrans for applications in material and life sciences were synthesized via palladium-mediated cyanation, carbonylation and Sonogashira cross-coupling starting from bromo-substituted naphthopyran 1 and benzopyrans 2a/b. A novel photoswitchable benzopyran-based omega-amino acid 6 for Fmoc-based solid-phase peptide synthesis is presented. The photochromic behaviour of the 3-cyano-subs...

Depending on the substitution pattern and the solvent, the gold-catalyzed cyclization of alk-4-yn-1-ones affords different oxygen heterocycles under mild reaction conditions. Alkynones with one substituent at C-3 undergo a 5-exo-dig cycloisomerization to substituted furans , whereas a 6-endo-dig cyclization to 4H-pyrans is observed with substrates bearing two substituents at C-3. In alcoholic s...

In the title compound, C(25)H(25)NO(4), the pyrrolidine ring exhibits an envelope conformation and the tetra-hydro-pyran ring exhibits a half-chair conformation. The crystal structure is stabilized by inter-molecular C-H⋯π inter-actions.

A trinuclear gold(I)-oxo complex, [(Ph3PAu)3O]BF4, serves as the catalyst for the stereocontrolled synthesis of 2-hydroxy-3,6-dihydropyrans from propargyl vinyl ethers. Importantly, the rearrangement proceeds with excellent diastereoselectivity, and the rearrangement of chiral nonracemic propargyl vinyl ethers proceeds with excellent chirality transfer to furnish enantioenriched pyrans. Additio...

In the title compound, C(10)H(5)FO(3), the chromenone ring is essentially planar, with a maximum deviation of 0.039 (1) Å. The dihedral angle between the fluoro-subsituted benzene ring and the pyran ring is 1.92 (4)°. In the crystal, mol-ecules are connected via weak inter-molecular C-H⋯O hydrogen bonds, forming supra-molecular ribbons along the b axis. These ribbons are stacked down the a axis.

The asymmetric unit of the title solvate, C(20)H(25)ClO(9)S·0.25CH(3)OH, contains one galactopyranosyl derivative and one-quarter of a methanol solvent mol-ecule. The galactopyran-ose ring is in the usual (4)C(1) conformation, and the anomeric center of the sugar has a β configuration. The value of θ (3.44°) and the range of torsion angles [or 53.1 (5)-63.0 (5)°] reflect a slight distortion of ...

In the title compound, C(25)H(25)NO(3), the dihydro-pyran ring adopts a half-chair conformation, whereas the pyrrolidine ring is in a twist conformation. The tolyl group is oriented at an angle of 82.92 (7)° with respect to the napthalene ring system. In the crystal structure, mol-ecules are linked into centrosymmetric dimers by C-H⋯π inter-actions involving the benzene ring of the tolyl group.

The Prins reaction was investigated using BF₃.OEt₂ as a Lewis acid. It has been recently demonstrated, that if BF₃.OEt₂ is used in stoichiometric amounts then these reactions generate fluorinated products where the BF₃.OEt₂ contributes fluoride ion to quench the intermediate carbocations. In this study oxa- and aza-Prins reactions for the synthesis of 4-fluoro-pyrans and -piperidines were inves...