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The asymmetric synthesis of ent-ketorfanol from simple and commercially available precursors is reported. A Rh(I) -catalyzed intramolecular CH alkenylation/torquoselective 6π electrocyclization cascade provides a fused bicyclic 1,2-dihydropyridine as a key intermediate. Computational studies were performed to understand the high torquoselectivity of the key 6π electrocyclization. The computational results demonstrate that a conformational effect is responsible for the observed selectivity. The ketone functionality and final ring are introduced in a single step by a redox-neutral acid-catalyzed rearrangement of a vicinal diol to give the requisite carbonyl, followed by intramolecular Friedel-Crafts alkylation.

The first example of C alkylation of 1,2-dihydropyridines with alkyl triflates and Michael acceptors was developed to introduce quaternary carbon centers with high regio- and diastereoselectivity. Hydride or carbon nucleophile addition to the resultant iminium ion also proceeded with high diastereoselectivity. Carbon nucleophile addition results in an unprecedented level of substitution to provide piperidine rings with adjacent tetrasubstituted carbon atoms.

Si(mply) rips it apart: C-F activation of fluorobenzene has been achieved using the extremely strong silyl Lewis acids [Et3Si(X)]+ (X=PhF or Et3SiH) and [(2,6-dixylyl-C6H 3)SiMe2] + paired with the anion CHB 11Cl11-. They abstract fluoride from unactivated fluorobenzene to give arylated products, consistent with phenyl-cation-like reactivity (see scheme). © 2010 Wiley-VCH Verlag GmbH & Co. KGaA.

Si(mply) rips it apart: C-F activation of fluorobenzene has been achieved using the extremely strong silyl Lewis acids [Et3Si(X)]+ (X=PhF or Et3SiH) and [(2,6-dixylyl-C6H 3)SiMe2] + paired with the anion CHB 11Cl11-. They abstract fluoride from unactivated fluorobenzene to give arylated products, consistent with phenyl-cation-like reactivity (see scheme). © 2010 Wiley-VCH Verlag GmbH & Co. KGaA.

Sly silyl caught in the act: Protonation of a mesitylene ring by the strongly acidic arenium carborane [CH(3)C(6)H(6)]- [CHB(11)Me(5)Br(6)] initiates a cascade reaction that results in a stable beta-silyl allyl cation (see picture, H yellow, C blue, silyl allyl group red). Remarkably, the driving force in the reaction suffices to disrupt a stable aromatic ring in favor of a cationic reactive intermediate.

The synthesis of monocarborane sulfonamides is reported. The methodology relies on coupling of the anionic {CB11} boron cluster to sulfonyl azides. Under rhodium catalysis and with the assistance of a pyridine or pyrimidine directing group at the C1 position, the cluster undergoes B−H activation. Conditions have been identified that lead to B2‐selective mono‐sulfonamidation with concomitant loss of N2. The protocol requires no additional ligand, oxidant or base and enables B−N bond formation with various monocarborane and sulfonyl azide inputs. The new products possess the structure [1‐(heteroaryl)‐2‐(NHSO2Ar)−CB11H10]− and have been fully characterized by NMR spectroscopy and mass spectrometry. In addition, three solid state structures confirm the particular B2 substitution pattern. Furthermore, the stoichiometric reaction of the pyridinyl monocarborane precursor with Rh(III) affords a cyclometalated complex with a direct B−Rh bond that has also been characterized by X‐ray crystallography. [ABSTRACT FROM AUTHOR]

Penta-iodination of the B2–6 positions of the {CB11} monocarborane cluster is reported. Products of the structure [2,3,4,5,6-I5-CB11H6-12-X]− (X = H, Me, Et, Ph, Br, I) were obtained and fully characterized. X-ray crystal structures of three new compounds confirm this particular substitution pattern. The synthetic method relies on palladium catalysis/B–H activation, assisted by the C1-COOH directing group. The one-pot procedure enables penta-iodination and subsequent decarboxylation under convenient conditions. The B2–6 regioselectivity is complementary to the commonly observed reactivity of {CB11} clusters, which follows the trend B12 > B7–11 > B2–6 for electrophilic substitution. Thus, for the first time upper-belt halogenation is achieved without prior modification of the lower-belt positions. [ABSTRACT FROM AUTHOR]

The efficient separation of acetylene (C2H2) from carbon dioxide (CO2) and CnH4 (n = 1 and 2) to manufacture high purity C2H2 and recover other light hydrocarbons is technologically important, while posing significant challenges. Herein, we reported a new TiF62− anion (TIFSIX) pillared metal-organic framework (MOF) ZNU-5 (ZNU = Zhejiang Normal University) with ultramicropores for highly selective C2H2 capture with low adsorption heat through gate opening based molecular sieving effect. ZNU-5 takes up a large amount of C2H2 (128.6 cm3/g) at 1.0 bar and 298 K but excludes CO2, CH4, and C2H4. Such high capacity has never been realized in MOFs with molecular sieving. The breakthrough experiments further confirmed the highly selective C2H2 separation performance from multi-component gas mixtures. 3.3, 2.8, and 2.2 mmol/g of C2H2 is captured at ZNU-5 from equimolar C2H2/CO2, C2H2/CO2/CH4, and C2H2/CO2/CH4/C2H4 mixtures, respectively. Furthermore, 2.6, 2.0, and 1.5 mmol/g of > 98% purity C2H2 can be recycled from the desorption process. Combining high working capacity, low adsorption heat, as well as good recyclability, ZNU-5 is promising for C2H2 purification. [ABSTRACT FROM AUTHOR]

Regioselective, five-fold B–H activation of the monocarborane cluster [CB11H12]− at the positions B7–11 has been accomplished. Selective substitution of these positions by B–H activation has not been reported before. Our protocol involves directing group assistance by the carboxylic acid functionality and is based on palladium catalysis using iodoarene coupling partners. Penta-arylated products are obtained in a single step with yields ranging from 42% to 89% and with good functional group tolerance. X-Ray crystal structures for five new compounds confirm the selective substitution of the lower belt of the monocarborane cage. [ABSTRACT FROM AUTHOR]

The Sonogashira cross coupling between the monocarborane cluster 12-ethynylmonocarba-closo-dodecaborate [CB11H11-12-C≡CH]− and bromoarenes under Pd catalysis has been developed, providing access to aryl carboranyl alkynes in yields of 42–95%. The transformations proceed under mild conditions and with high functional group tolerance using commercially available coupling partners. X-ray structural analyses and the identification of an unusual phosphonium zwitterion byproduct are reported as well. [ABSTRACT FROM AUTHOR]

The lithiacarborane [Li−CB11H11]− plays a central role in carborane chemistry, as it is a key intermediate to achieve the selective functionalization of the monocarba‐closo‐dodecaborate [CB11H12]− for applications in various fields. Also, it is an organometallic species of fundamental interest because it represents a 3D analogue of phenyllithium featuring an exo C−Li bond in addition to the delocalized negative endo charge of the spherical cluster. For the first time, the elusive and highly reactive endo/exo formal dianion [CB11H11]2− has been isolated as its lithiate as well as zincate in pure form and fully characterized. DFT calculations corroborate the experimental findings and underscore the remarkably high reactivity of the lithiacarborane. Subsequent derivatizations demonstrate the relevance of its initial clean formation. [ABSTRACT FROM AUTHOR]

The lithiacarborane [Li−CB11H11]− plays a central role in carborane chemistry, as it is a key intermediate to achieve the selective functionalization of the monocarba‐closo‐dodecaborate [CB11H12]− for applications in various fields. Also, it is an organometallic species of fundamental interest because it represents a 3D analogue of phenyllithium featuring an exo C−Li bond in addition to the delocalized negative endo charge of the spherical cluster. For the first time, the elusive and highly reactive endo/exo formal dianion [CB11H11]2− has been isolated as its lithiate as well as zincate in pure form and fully characterized. DFT calculations corroborate the experimental findings and underscore the remarkably high reactivity of the lithiacarborane. Subsequent derivatizations demonstrate the relevance of its initial clean formation. [ABSTRACT FROM AUTHOR]