Synlett

Herein, we present a rapid and efficient method for synthesizing cyclic acetals and ketals utilizing a rotary evaporator. Unlike the conventional Dean–Stark dehydration process, which typically demands extended reaction times and copious amounts of organic solvents, our approach affords the synthesis of cyclic acetals and ketals with varying ring sizes in 30 min while using minimal quantities of dimethyl sulfoxide as the solvent. This innovative protocol features high yields, fast reactions, easy operation, and broad substrate applicability.

An expedient and easy-to-handle synthetic platform has been established for the constructing of 2H-thiophenes carrying fluorine atoms through [4+1] cyclization of enaminothiones with fluorinated carbene precursors. This simple reaction system is well compatible with a wide range of substrates under completely metal-free conditions. The resulting 2H-thiophenes can undergo further late-stage modifications to yield a wide range of fluorine-substituted heterocycles.

Catalytic C–H activation reactions are now established as a means to directly transform organic molecules and are commonly associated with metals such as palladium, rhodium, ruthenium and iridium. This Account will describe a short number of reports demonstrating that structures containing main group elements can facilitate C–H activation processes. In particular, boron-based catalysts can promote catalytic arene C–H borylation reactions, and an emerging approach using phosphenium ions can also cleave sp2 C–H bonds. These processes use a Lewis acidic main group atom combined with a pendant base to cleave C–H bonds, which compares with metal-catalyzed reactions that proceed via concerted metalation deprotonation mechanisms.1 Introduction2 Metal-Catalyzed C–H Activation via CMD/AMLA Mechanisms3 C–H Borylation via Boron-Based Catalysts4 C–H Activation Using Phosphenium Ions5 Conclusions

We report a unique synthetic route to benzo[7]annulene derivatives. When benzylidene malonates having a 1-(N,N-dialkylamino)alkyl group at the ortho-position are treated with a stoichiometric amount of M(OTf)3 (M = Sc, Yb, Gd), three transformations ([1,4]-hydride shift/isomerization into an enamine/intramolecular Stork enamine acylation) proceed sequentially to afford various benzo[7]annulene derivatives in moderate chemical yields. To our knowledge, the present reaction is the first example of an internal redox reaction involving a [1,n]-hydride shift/(n+3)-cyclization process.

Palladium-catalyzed asymmetric [3+2] cycloaddition reaction of vinyl cyclopropane and electron-deficient dienes was realized. The cycloaddition reaction proceeded regioselectively on the distant C=C double bond of electron-deficient dienes, and was mainly controlled by the steric hindrance of the 5-substituent of electron-deficient dienes. Chiral multi-substituted cyclopentanes bearing three functional groups (monosubstituted alkene, conjugated ester, and cyano) and three continuous stereocenters were obtained in moderate to high yields, diastereoselectivities, and enantioselectivities.

Herein, an atom-economic method for the synthesis of fused-ring pyrrolizine derivatives by a cycloaddition reaction of easily accessible N-substituted pyrrole-2-carboxaldehydes with N-substituted maleimides in the presence of di-tert-butyl peroxide has been successfully developed. A total of 23 compounds were obtained by using this method, with a maximum yield of 72%, providing a practical and efficient method for the synthesis of tricyclic pyrrolizine frameworks.

An allylic side chain is introduced onto a chiral γ-amino-β-ketoamide by a Pd-catalyzed allylic alkylation. Subsequent ozonolysis and oxidation proceed only with Cbz-protected ketoamides. The total synthesis of moiramide B is finalized by peptide coupling.

A diaminocyclopentadienone ruthenium complex allows control of regioselectivity in the ruthenium-catalyzed isomerization of propargyl alcohols through the choice of additive. Thereby, both products of the Meyer–Schuster rearrangement and redox isomerization products are selectively accessible. In the presence of hydroxylamine-O-sulfonic acid, unsaturated nitriles are formed instead. The ruthenium catalyst is readily available and stable to moisture, air, and acidic conditions.

1,1-Diborylalkene, a class of important diboryl species, serves as the synthetic precursor of multisubstituted olefin, which is a prevalent building block in natural products, functional materials, and pharmaceuticals. Current methods mainly afford symmetrical 1,1-diborylalkenes, and late-stage differentiation of the two identical boryl groups is required to achieve selective difunctionalization. In comparison, stereoselective synthesis of unsymmetrical 1,1-diborylalkenes (UDBA) are less-explored. This Synpacts article provides a brief summary of the achievements in the synthesis of UDBAs. In particularly, we highlight our recent work on the unsymmetrical 1,1-diborylation of alkynes using a neutral sp2–sp3 diboron reagent to access UDBAs and their controllable stepwise derivatization.1 Introduction2 Background: Unsymmetrical 1,1-Diborylalkene Synthesis3 Stereoselective Unsymmetrical 1,1-Diborylation of Alkynes with a Neutral sp2–sp3 Diboron Reagent4 Summary and Outlook

Organic chromophores emerged as diverse functional materials in the areas of organic catalysis, toxic materials sensing, bio-imaging, and organic electronic devices. With rich chemical and electronic structures, main-group elements have been extensively implanted in organic chromophores to fine-tune the chemical/electronic structures and optoelectronic properties. In this Synpact article, we present a concise overview of the development of phosphorus (P)-containing organic chromophores, further highlighting our recent contributions in the field. A new aspect of combining the P element with the indole moiety was pursued to construct a new series of seven-membered P-organic chromophores; namely, indole-functionalized phosphepines. The new combination endowed the system with rich chemical and electronic structures, for which intriguing photophysical properties were consequently revealed. The combination provided an efficient synthetic protocol to access new P-heterocycles and also offered a new strategy to design functional organic chromophores.