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A catalytic asymmetric α-hydroxylation of pyridinone-fused lactones, containing the core structure of camptothecin, is described. Development of a novel spiropyrrolidine amide (SPA) derived triazolium bromide organo-cation catalyst is crucial for a highly enantioselective oxidation, which also accommodates a wide array of lactones with various substituents. The resulting tricyclic tertiary alcohol with an oxa-quaternary carbon center can be further applied in the synthesis of SN-38 and irinotecan, two anti-cancer drugs derived from camptothecin. [ABSTRACT FROM AUTHOR]

A photoinduced reductive Reformatsky reaction by cooperative dual-metal catalysis is described. This methodology enables the implementation of this venerable reaction in environmentally friendly conditions, obviating the need for a stoichiometric amount of metals. A broad range of synthetically useful β-hydroxy esters can be efficiently prepared in moderate to high yields using this protocol. [ABSTRACT FROM AUTHOR]

A facile and environmentally benign KI(cat.)/NaBO3·4H2O oxidation system has been developed for the tandem oxidative aminocyclization/coupling of tryptamines, affording a series of 3a,3a′-bispyrrolidino[2,3-b]indolines with high efficiency (up to 94% yield). This reaction features an electrophilic "I+" mechanism, which is importantly quite different from and milder than the typical radical-involving process, and can be readily amplified for the total synthesis of (+)-WIN 64821. [ABSTRACT FROM AUTHOR]

An SPA-triazolium bromide-catalyzed transannular C-acylation of enol lactones is presented. This methodology provides convenient access to a range of enantioenriched spirocyclic 1,3-diketones in moderate to high yields and enantioselectivities and features a broad substrate scope in terms of enol lactones. The catalytic capability of this triazolium salt catalyst is also demonstrated in this enantioselective transformation, which could inspire its further application. [ABSTRACT FROM AUTHOR]

A facile and efficient method to form a chiral multi-substituted 3H-spiro[benzofuran-2,1′-cyclopentane] structural unit has been developed via a one-pot [3+2] cyclization/semipinacol rearrangement cascade. A catalysis system of Cu(ii)/BOX has been used to efficiently construct a key stereogenic center via a cyclization between substituted benzoquinones and allylic alcohols affording the desired products in good yields and with excellent enantioselectivities and diastereoselectivities (21 examples; up to 67% yields; up to 92% ee and up to ＞20 : 1 dr). This method provides an alternative strategy for the synthesis of the corresponding bioactive molecules containing spiro[benzofurancyclopentane] skeleton units. [ABSTRACT FROM AUTHOR]

Transition-metal-free α-arylation of α-nitroketones with diaryliodonium salts has been realized for the first time. As an application of this methodology, a concise synthesis of the clinical drug tiletamine was also achieved via a three-step procedure from 2-nitrocyclohexanone without the isolation of intermediates. [ABSTRACT FROM AUTHOR]

A tandem C–H oxidation/oxa-[3,3] Cope rearrangement/aldol reaction of allylic silylethers promoted by T+BF4−(tempo oxoammonium tetrafluoroborate)/ZnBr2 has been successfully developed allowing the efficient construction of 8-oxabicyclo[3.2.1]octanes and their analogs with a wide substrate scope. [ABSTRACT FROM AUTHOR]

1,2-Carbon atom rearrangement has been broadly applied as a guiding strategy in complex molecule assembly. As it entails the carbon–carbon or carbon–heteroatom bond migration between two vicinal atoms, this type of reaction is capable of generating structural complexity through a molecular skeletal reorganization. This review will focus on recent employment of this strategy in the total synthesis of natural products, highlighting the exceptional utility of such synthetic methodologies in the construction of intricate carbocycles, heterocycles or structurally complex motifs from synthetically more accessible precursors. [ABSTRACT FROM AUTHOR]

The direct and efficient construction of α-aryl-β-substituted cyclic ketone scaffolds has been achieved using a Cu-mediated one-pot Michael addition/α-arylation strategy. The reaction features easily available materials, broad substrate scope, moderate to good yield, and an excellent diastereoselectivity. [ABSTRACT FROM AUTHOR]

Radical aryl migration reactions are of particular interest to the chemical community due to their potential application in radical chemistry and organic synthesis. The neophyl rearrangements used as radical clocks for examining the radical–molecular reactions have been known for decades. The combinations of these migrations with other radical reactions have provided a wide range of novel synthetic methodologies that are complementary to nucleophilic rearrangements. This review will give an overview of various types of radical aryl migrations, with an emphasis on their mechanistic studies from a historical point of view, as well as their application in tandem radical reactions. [ABSTRACT FROM AUTHOR]

A novel chiral spiro-pyrrolidine silyl ether organocatalyst has been designed. Its catalytic asymmetric effect is demonstrated by the Michael addition reaction, which affords the desired products with an all-carbon quaternary center in up to 99% ee and 87% yield. Furthermore, the reaction process has been investigated via in situ NMR experiments. [ABSTRACT FROM AUTHOR]

A novel propargylic electrophile-induced tandem intermolecular addition–semipinacol rearrangement was developed efficiently under mild conditions. Various allylic silylether substrates as well as Co-complexed propargylic species were applicable to this protocol and gave a series of synthetically useful β-propargyl spirocyclic ketones in moderate to good yields. Its synthetic application was also demonstrated by an efficient construction of the key tricyclic moiety of daphlongamine E. [ABSTRACT FROM AUTHOR]

Tandem reactions of cis-2-acyl-1-alkynyl-1-aryl cyclopropanes 1tuned by gold(i) and silver(i) catalysts are described, which afford selectively the key pyran-fused indene cores 2and the 2,4,6-trisubstituted phenols 3in good yields, respectively. [ABSTRACT FROM AUTHOR]

An unusual cascade C-H activation, vinylation and 6π-electrocyclization of 2-pyridyl aldimines with vinyl bromides/triflates was achieved using catalysis with a unique CCC pincer NHC-Ru(iii) complex (Cat B). This reaction was found to enable a rapid and diverse synthesis of polycyclic 4 H -pyrido[1,2- a ]pyrimidine derivatives in mostly good to high yields, and with a broad substrate scope. A mechanistic study suggested the formation of a semi-opened Ru(iii) intermediate chelating/activating the aldimine, and the occurrence of single-electron transfer (SET) to generate a vinyl radical, followed by vinylation and then an intramolecular 6π-electrocyclization of 1 N ,3 N -hexatrene to form the product. This protocol provides a convenient approach for preparing and seeking new drug candidates., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

A novel polyene cyclization using the allene group as the initiator has been successfully developed. This methodology provides an efficient strategy for the construction of an abietane-type tricyclic skeleton with a functionalizable C2-C3 double bond and features a wide substrate scope and excellent stereoselectivities. Potential utility of this approach has been well demonstrated by the collective total synthesis of seven abietane-type diterpenoids. Specifically, (±)-2,3-dihydroxyferruginol and (±)-2,3-dihydroxy-15,16-dinor- ent -pimar-8,11,13-triene were synthesized for the first time., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Transition-metal-free α-arylation of α-nitroketones with diaryliodonium salts has been realized for the first time. As an application of this methodology, a concise synthesis of the clinical drug tiletamine was also achieved via a three-step procedure from 2-nitrocyclohexanone without the isolation of intermediates.

A catalytic intermolecular semipinacol rearrangement induced by allylic carbocations has been realized. This tandem reaction is highly efficient under the catalysis of ZnBr 2 , generating a wide range of α-homoallyl substituted ketones which contain all-carbon quaternary centres in good to excellent yields (up to 98%) with moderate to high diastereoselectivities (up to >20 : 1). Synthetic application of this novel methodology in the construction of core structures of natural products is also reported.

A novel and efficient tandem S N 2' nucleophilic substitution/oxidative radical cyclization reaction of aryl substituted allylic alcohols with 1,3-dicarbonyl compounds has been developed by using Mn(OAc) 3 as an oxidant, which enables the expeditious synthesis of polysubstituted dihydrofuran (DHF) derivatives in moderate to high yields. The use of weakly acidic hexafluoroisopropanol (HFIP) as the solvent rather than AcOH has successfully improved the yields and expanded the substrate scope of this type of radical cyclization reactions. Mechanistic studies confirmed the cascade reaction process involving a final radical cyclization.