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Synthesis of bicyclic scaffolds has attracted tremendous attention because they are playing an important role as saturated bioisosteres of benzenoids in modern drug discovery. Here, we report a BF3‐catalyzed [2π+2σ] cycloaddition of aldehydes with bicyclo[1.1.0]butanes (BCBs) to access polysubstituted 2‐oxabicyclo[2.1.1]hexanes. A new kind of BCB containing an acyl pyrazole group was invented, which not only significantly facilitates the reactions, but can also serve as a handle for diverse downstream transformations. Furthermore, aryl and vinyl epoxides can also be utilized as substrates which undergo cycloaddition with BCBs after in situ rearrangement to aldehydes. We anticipate that our results will promote access to challenging sp3‐rich bicyclic frameworks and the exploration of BCB‐based cycloaddition chemistry. [ABSTRACT FROM AUTHOR]

"Through space" palladium/hydrogen shift is an efficient strategy to achieve selective functionalization of a specific remote C−H bond. Compared with relatively extensive exploited 1,4‐palladium migration process, the relevant 1,5‐Pd/H shift was far less investigated. We herein report a novel 1,5‐Pd/H shift pattern between a vinyl and an acyl group. Through the pattern, rapid access to 5‐membered‐dihydrobenzofuran and indoline derivatives has been achieved. Further studies have unveiled an unprecedented trifunctionalization (vinylation, alkynylation and amination) of a phenyl ring through 1,5‐palladium migration relayed decarbonylative Catellani type reaction. A series of mechanistic investigations and DFT calculations have provided insights into the reaction pathway. Notably, it was unveiled that the 1,5‐palladium migration in our case prefers a stepwise mechanism involving a PdIV intermediate. [ABSTRACT FROM AUTHOR]

Multiblock copolymers are envisioned as promising materials with enhanced properties and functionality compared with their diblock/triblock counterparts. However, the current approaches can construct multiblock copolymers with a limited number of blocks but tedious procedures. Here, we report a thioester‐relayed in‐chain cascade copolymerization strategy for the easy preparation of multiblock copolymers with on‐demand blocks, in which thioester groups with on‐demand numbers are built in the polymer backbone by controlled/living polymerizations. These thioester groups further serve as the in‐chain initiating centers to trigger the acyl group transfer ring‐opening polymerization of episulfides independently and concurrently to extend the polymer backbone into multiblock structures. The compositions, number of blocks, and block degree of polymerization can be easily regulated. This strategy can offer easy access to a library of multiblock copolymers with ≈100 blocks in only 2 to 4 steps. [ABSTRACT FROM AUTHOR]

Taxol is a clinically used drug for the treatment of various types of cancers. Its 6/8/6/4‐membered ring (ABCD‐ring) system is substituted by eight oxygen functional groups and flanked by four acyl groups, including a β‐amino acid side chain. Here we report a 34‐step total synthesis of this unusually oxygenated and intricately fused structure. Inter‐ and intramolecular radical coupling reactions connected the A‐ and C‐ring fragments and cyclized the B‐ring, respectively. Functional groups of the A‐ and C‐rings were then efficiently decorated by employing newly developed chemo‐, regio‐, and stereoselective reactions. Finally, construction of the D‐ring and conjugation with the β‐amino acid delivered taxol. The powerful coupling reactions and functional group manipulations implemented in the present synthesis provide new valuable information for designing multistep target‐oriented syntheses of diverse bioactive natural products. [ABSTRACT FROM AUTHOR]

We developed a chiral symmetry breaking method for monoacylated meso diols. The X‐ray crystal structure analysis of monoacylated 1,4‐anhydroerythritols, meso cyclic diols with a cis configuration, revealed that the O‐(p‐anisoyl) derivative crystallized as a racemic conglomerate of the P212121 crystal system. It was confirmed that the substrate racemized by intramolecular transfer of the acyl group in the presence of a catalytic amount of base. Evaporating the solvent gradually from the solution or Viedma ripening to promote crystallization‐induced deracemization efficiently led to enantiomer crystals. These results provide the first successful example of asymmetric expression and amplification by deracemization of sugar derivatives without an external chemical chiral source. Furthermore, we applied this methodology to acyclic meso‐1,2‐diols. Three O‐monoacylated substrates were successfully deracemized to 99 % ee by Viedma ripening. We also developed asymmetric desymmetrization of meso‐1,2‐diols by combining acylation and crystallization‐induced deracemization. [ABSTRACT FROM AUTHOR]

The stereoselective introduction of the glycosidic bond remains one of the main challenges in carbohydrate synthesis. Characterizing the reactive intermediates of this reaction is key to develop stereoselective glycosylation reactions. Herein we report the characterization of low‐populated, rapidly equilibrating mannosyl dioxanium ions that arise from participation of a C‐3 acyl group using chemical exchange saturation transfer (CEST) NMR spectroscopy. Dioxanium ion structure and equilibration kinetics were measured under relevant glycosylation conditions and highly α‐selective couplings were observed suggesting glycosylation took place via this elusive intermediate. [ABSTRACT FROM AUTHOR]

A method is described for the isomerization of acyclic allylic alcohols into β‐functionalized ketones via 1,3‐alkyl transposition. This reaction proceeds via light‐driven proton‐coupled electron transfer (PCET) activation of the O−H bond in the allylic alcohol substrate, followed by C−C β‐scission of the resulting alkoxy radical. The transient alkyl radical and enone acceptor generated in the scission event subsequently recombine via radical conjugate addition to deliver β‐functionalized ketone products. A variety of allylic alcohol substrates bearing alkyl and acyl migratory groups were successfully accommodated. Insights from mechanistic studies led to a modified reaction protocol that improves reaction performance for challenging substrates. [ABSTRACT FROM AUTHOR]

Gold‐catalyzed reactions of alkynyl N‐sulfinylimines were used to produce the corresponding 2H‐azirines possessing sulfenyl and acyl groups at the 3‐position of the azirine ring in good to excellent yields. These reactions involved internal transfer of the sulfinyl oxygen atom to form a thiooxime intermediate tethered to an α‐oxo gold carbene moiety. Subsequent insertion of the carbene into the N−S bond resulted in ring construction. [ABSTRACT FROM AUTHOR]

Rearrangement reactions incorporated into cascade reactions play an important role in rapidly increasing molecular complexity from readily available starting materials. Reported here is a Cu‐catalyzed cascade reaction of α‐(hetero)aryl‐substituted alkyl (hetero)aryl ketones with primary amines that incorporates an unusual 1,2‐aryl migration induced by amide C−N bond formation to produce a class of structurally novel α,α‐diaryl β,γ‐unsaturated γ‐lactams in generally good‐to‐excellent yields. This cascade reaction has a broad substrate scope with respect to primary amines, allows a wide spectrum of (hetero)aryl groups to smoothly undergo 1,2‐migration, and tolerates electronically diverse α‐substituents on the (hetero)aryl ring of the ketones. Mechanistically, this 1,2‐aryl migration may stem from the intramolecular amide C−N bond formation which induces nucleophilic migration of the aryl group from the acyl carbon center to the electrophilic carbon center that is conjugated with the resulting iminium moiety. [ABSTRACT FROM AUTHOR]

We report a solid‐phase strategy for total synthesis of the peptidic natural product yaku'amide B (1), which exhibits antiproliferative activity against various cancer cells. Its linear tridecapeptide sequence bears four β,β‐dialkylated α,β‐dehydroamino acid residues and is capped with an N‐terminal acyl group (NTA) and a C‐terminal amine (CTA). To realize the Fmoc‐based solid‐phase synthesis of this complex structure, we developed new methods for enamide formation, enamide deprotection, and C‐terminal modification. First, traceless Staudinger ligation enabled enamide formation between sterically encumbered alkenyl azides and newly designed phosphinophenol esters. Second, application of Eu(OTf)3 led to chemoselective removal of the enamide Boc groups without detaching the resin linker. Finally, resin‐cleavage and C‐terminus modification were simultaneously achieved with an ester–amide exchange reaction using CTA and AlMe3 to deliver 1 in 9.1 % overall yield (24 steps from the resin). [ABSTRACT FROM AUTHOR]

Indoles are privileged heterocycles found in many biologically active pharmaceuticals and natural products. However, the selective functionalization of the benzenoid moiety in indoles in preference to the more reactive pyrrolic unit is a significant challenge. Herein we report that N‐acyl directing groups enable the C7‐selective C−H borylation of indoles using just BBr3. This transformation shows some functional‐group tolerance and notably proceeds with C6 substituted indoles. The directing group can be readily removed in situ and the products isolated as the pinacol boronate esters. Acyl‐directed electrophilic borylation can be extended to carbazoles and anilines with excellent ortho selectivity. 4‐amino‐indoles are amenable to this process, with acyl group installation and directed electrophilic C−H borylation enabling selective formation of C5‐BPin‐indoles. [ABSTRACT FROM AUTHOR]

Indoles are privileged heterocycles found in many biologically active pharmaceuticals and natural products. However, the selective functionalization of the benzenoid moiety in indoles in preference to the more reactive pyrrolic unit is a significant challenge. Herein we report that N‐acyl directing groups enable the C7‐selective C−H borylation of indoles using just BBr3. This transformation shows some functional‐group tolerance and notably proceeds with C6 substituted indoles. The directing group can be readily removed in situ and the products isolated as the pinacol boronate esters. Acyl‐directed electrophilic borylation can be extended to carbazoles and anilines with excellent ortho selectivity. 4‐amino‐indoles are amenable to this process, with acyl group installation and directed electrophilic C−H borylation enabling selective formation of C5‐BPin‐indoles. [ABSTRACT FROM AUTHOR]

A RhIII-catalyzed intramolecular oxidative cross-coupling between double bonds for the synthesis of macrolides is described. Under the optimized reaction conditions, macrocycles containing a diene moiety can be formed in reasonable yields and with excellent chemo- and stereoselectivity. This method provides an efficient approach to synthesize macrocyclic compounds containing a 1,3-conjugated diene structure. [ABSTRACT FROM AUTHOR]

In metabolic glycoengineering (MGE), cells or animals are treated with unnatural derivatives of monosaccharides. After entering the cytosol, these sugar analogues are metabolized and subsequently expressed on newly synthesized glycoconjugates. The feasibility of MGE was first discovered for sialylated glycans, by using N-acyl-modified mannosamines as precursor molecules for unnatural sialic acids. Prerequisite is the promiscuity of the enzymes of the Roseman-Warren biosynthetic pathway. These enzymes were shown to tolerate specific modifications of the N-acyl side chain of mannosamine analogues, for example, elongation by one or more methylene groups (aliphatic modifications) or by insertion of reactive groups (bioorthogonal modifications). Unnatural sialic acids are incorporated into glycoconjugates of cells and organs. MGE has intriguing biological consequences for treated cells (aliphatic MGE) and offers the opportunity to visualize the topography and dynamics of sialylated glycans in vitro, ex vivo, and in vivo (bioorthogonal MGE). [ABSTRACT FROM AUTHOR]

A nickel/N-heterocyclic carbene catalytic system has been established for decarbonylative borylation of amides with B2nep2 by C−N bond activation. This transformation shows good functional-group compatibility and can serve as a powerful synthetic tool for late-stage borylation of amide groups in complex compounds. More importantly, as a key intermediate, the structure of an acyl nickel complex was first confirmed by X-ray analysis. Furthermore, the decarbonylative process was also observed. These findings confirm the key mechanistic features of the acyl C−N bond activation process. [ABSTRACT FROM AUTHOR]

A correction to the article "Visible-Light-Mediated 1,2-Acyl Migration: The Reaction of Secondary Enamino Ketones with Singlet Oxygen" that was published in the 2014 issue is presented.