Rhodium(I)‐Catalyzed Cyclization of Allenynes with a Carbonyl Group through Unusual Insertion of a CO Bond into a Rhodacycle Intermediate

Rhodium(I)‐catalyzed cyclization of allenynes with a tethered carbonyl group was investigated. An unusual insertion of a C?O bond into the C(sp²)–rhodium bond of a rhodacycle intermediate occurs via a highly strained transition state. Direct reductive elimination from the obtained rhodacyle intermediate proceeds to give a tricyclic product containing an 8‐oxabicyclo[3.2.1]octane skeleton, while β‐hydride elimination from the same intermediate gives products that contain fused five‐ and seven‐membered rings in high yields.     

Metal Alkoxide Promoted Regio‐ and Stereoselective CO and CC Metathesis of Allenoates with Aldehydes

The reaction of 2,3‐allenoates and aldehydes in the presence of an alkoxide affords alkyl 4,5‐diaryl‐3‐oxo‐2‐propylpent‐4(E)‐enoates and cis‐3,4‐diaryloxetanes through a formal C?O and C?C metathesis. A mechanism for this reaction has been proposed.     

Molecular and Crystal Structure of Magnolol—C18H18O2

Magnolol, 2, 2′-dihydroxy-5, 5′-diallylbiphenyl (C₁₈H₁₈O₂) was isolated from the heartwood of Taiwan sassafras, Sassafras randaiense (Hay.) Rehd. (Lauraceae) and characterized by single crystal X-ray diffraction. It crystallized in monoclinic P 2₁/C. The cell parameters are a=10.905(3), b=8.834(4), c=16.103(9) Å, β=106.76°(3), z=4. The structure was solved by direct method. The dihedral angle between two benzene rings is about 45′ which seems to be the best arrangement for intra- and inter-molecular H-bondings. O … O distances are ～2.6 Å which indicate very strong H-bonding. The solid structure can be discribed as a helix chain of molecules connected through H-bonds parallel to b-axis.     

Chemical Tricks To Stabilize Silanones and Their Heavier Homologues with EO Bonds (E=Si–Pb): From Elusive Species to Isolable Building Blocks

In contrast to the well‐established chemistry of ketones (R₂C?O), the reactivity of the elusive heavier congeners R₂E?O (E=Si, Ge, Sn, Pb) is far less explored because of the high polarity of the E?O bonds and hence their tendency to oligomerize with no activation barrier. Very recently, great advances have been achieved in the synthesis of isolable compounds with E?O bonds, including the investigation of donor‐stabilized isolable silanones and the first stable “genuine” germanone. These compounds show drastically different reactivities compared to ketones and represent versatile building blocks in silicon–oxygen and germanium–oxygen chemistry. This and other exciting achievements are described in this Minireview.