Modular Synthesis of Multi-substituted Cyclobutanones Enabled by Oxyallyl Cations

Stereoselective synthesis of multi-substituted cyclobutanes with different substituents is still a daunting challenge in organic synthesis.We report here a practical and facile approach to synthesizing all-trans 2,3,4-trisubstituted cyclobutanones from readily available dichlorocyclobutanones.The substitution reaction proceeds smoothly via oxyallyl cation intermediates under mild basic conditions.Further transformation to the synthesis of 1,2,3,4-tetrasubstituted cyclobutanes was also explored.

One Stone for Three Birds-Rhodium-Catalyzed Highly Diastereoselective Intramolecular [4+2] Cycloaddition of Optically Active Allene-1,3-dienes

Summary of main observation and conclusion RhCI(PPh3)3-catalyzed [4+2] intramolecular cycloaddition of optically active axially chiral allene-dienes afforded c/s-fused [3.4.0]-bicyclic products with three chiral centers in good yields with an excellent chemo-and diastereoselectivity. A pair of enantiomers of such products was gen erated highly selectively from both ena ntiomers of starting allene-die nes, indicati ng that the axial chirality dictated the absolute configurations of the three in situ generated chiral centers with a very high efficiency of chirality transfer.

An Enantioselective Approach to Heteroatom-Containing Bicyclic Derivatives via Inverse-Electron-Demand Diels-Alder Reactions

Chiral heteroatom-containing bicyclic scaffolds are important pharmacophores and prevalent in bioactive natural products and drug molecules.Herein,we report a unified approach for the divergent synthesis of chiral heteroatom-containing bicyclic derivatives by lanthanide(lil)-catalyzed asymmetric inverse-electron-demand Diels-Alder reactions of 2-pyrones.These reactions occur with vari-ous readily available dihydropyrroles and dihydrofurans as dienophiles,providing a step-economical synthetic platform for densely functionalized ciss-hydroindoles and cis-hydrobenzofurans with excellent yields and enantioselectivities.The synthetic utility of this approach is demonstrated by the concise synthesis of(-)-α-lycorane and(-)-lycorine alkaloids.

The [4+2] Cycloaddition of 2-Pyrone in Total Synthesis

Diels-Alder reaction is one of the most important reactions in organic synthesis and has witnessed great achievements in total syntheses of complex natural products.In this review,we will focus on the [4+2] cycloaddition that utilizes 2-pyrone as the diene component.Major advances of its applications in the total syntheses of natural products in the past fifty years will be discussed here.

Dancing on Ropes-Enantioselective Functionalization of Preformed Four-Membered Carbocycles

Cyclobutane derivatives have been recognized as useful structural motifs in organic synthesis and drug design.With the revival of photochemistry,the enantioselective synthesis of cyclobutane derivatives using[2+2]-cycloadditions has garnered numerous attentions.On the other hand,enantioselec-tive functionalization of preformed four-membered carbocycles is emerging as an important complementary approach to access chiral cyclobutane de-rivatives with versatile structural patterns.Herein,we summarize recent advances in this field from 2012.To avoid undesired C—C bond cleavage driv-en by strain-releasing,it is crucial to choose compatible methods for enantioselective functionalization and meanwhile preserving intact four-membered ring skeleton.Guided by calculated hydrogenation enthalpies,which are used to evaluate the strain energy of indicated C—C bond,a clear picture of the developed methodologies on functionalization of four-membered carbocycles combining the strain energy and enhanced reactivity is presented.

Pd-Catalyzed 2,3-Allenylation of Oxindoles with 2,3-Allenylic Carbonates

Allenes and oxindoles are two classes of very important compounds for medicinal chemistry and organic chemistry.Thus,it is of high interest to combine an allene and an oxindole into one molecule.Herein,the first example of palladium-catalyzed exclusive 2,3-allenylation reaction of oxindoles with 2,3-allenylic carbonates has been successfully developed.A rationale for the selectivity of 2,3-allenylation over the expected 1,3-alkadienylation has been proposed.

Palladium-Catalyzed Coupling of Propargylic Alcohols with Boronic Acids under Ambient Conditions

Summary of main observation and conclusion A highly eficient palladium-catalyzed direct coupling of propargylic alcohols with organoboronic acids to synthesize tri-and tetra-substituted llenes has been developed under mild reaction conditions.Many useful functional groups are tolerated in this pro-cess with high to excellent yields.Preliminary biological studies showed that several tri-and tetra-substituted allenes exhibited potent anti-diabetic activi-ties.

Rh-Catalyzed Reaction of Propargylic Alcohols with Aryl Boronic Acids-Switch from β-OH Elimination to Protodemetalation

Summary of main observation and conclusion It is known that Rh-catalyzed reaction of propargyic alcohols with aryl metallic reagents undergoes Su2Z-type reaction affording alenes via a sequential arylmetalation andβ-OH elimination process.Here we report a Rh/Ag cocatalyed reaction of pro-pargylic alcohols with organoboronic acids affording stereo defined(E)-3-arlallylic alcohols via arylmetalation and protodemetalation with a high regio-and stereoselectivity under very mild conditions.The reaction exhibits a good substrate scope and the compatibility with synthetically useful functional groups with no racemization for optically active propargylic alcohols.Such a reaction may also be extended to homopropargylie alcohols with a remarka-ble regioselectivity and exclusive E-stereoselectity.