Copper(I)-catalyzed asymmetric 1,6-conjugate allylation

Catalytic asymmetric conjugate allylation of unsaturated carbonyl compounds is usually difficult to achieve, as 1,2-addition proceeds dominantly and high asymmetric induction is a challenging task. Herein, we disclose a copper(I)-NHC complex catalyzed asymmetric 1,6-conjugate allylation of 2,2-dimethyl-6-alkenyl-4H-1,3-dioxin-4-ones. The phenolic hydroxyl group in NHC ligands is found to be pivotal to obtain the desired products. Both aryl group and alkyl group at δ-position are well tolerated with the corresponding products generated in moderate to high yields and high enantioselectivity. Moreover, both 2-substituted and 3-substituted allylboronates serve as acceptable allylation reagents. At last, the synthetic utility of the products is demonstrated in several transformations by means of the versatile terminal olefin and dioxinone groups.

Synthetic Studies towards the Total Synthesis of Indole Alkaloids Containing Indolyl Lactam Frameworks

In this account, recent progress on the synthetic studies of several monoterpene indole alkaloids, (±)-mersicarpine, misassigned (±)-tronoharine, and (±)-leuconodines D and E, is summarized. Specifically, the rationale for the design and development of the Lewis acid catalyzed SN1-type substitution and formal [3+3] cycloaddition reaction of indol-2-yl carbinols, and the Pd-catalyzed aerobic oxidative intramolecular Heck cross-coupling of indolyl amides tethered with a terminal olefin functionality, are emphasized. These key reactions set the basis for the rapid construction of the fused ring skeleton containing an all-carbon quaternary center at the indol-2-yl position.1 Introduction2 Synthetic Study of (±)-Mersicarpine3 Synthetic Study of the Misassigned (±)-Tronoharine4 Study of the Asymmetric Reaction of Indol-2-yl Carbinols5 Synthetic Study of (±)-Leuconodines D and E6 Conclusion

Regioselective Gas-Phase n-Butane Transfer Dehydrogenation via Silica-Supported Pincer-Iridium Complexes

<b>Abstract:</b> The production of olefins via on-purpose dehydrogenation of alkanes allows for a more efficient, selective and lower cost alternative to processes such as steam cracking. Silica-supported pincer-iridium complexes of the form [(≡SiO-^R4POCOP)Ir(CO)] (^R4POCOP = κ³-C₆H₃-2,6-(OPR₂)₂) are effective for acceptorless alkane dehydrogenation, and have been shown stable up to 300 °C. However, while solution-phase analogues of such species have demonstrated high regioselectivity for terminal olefin production under transfer dehydrogenation conditions at or below 240 °C, in open systems at 300 °C, regioselectivity under acceptorless dehydrogenation conditions is consistently low. In this work, complexes <a>[(≡SiO-<i>^t</i>^Bu4POCOP)Ir(CO)] </a>(<b>1</b>) and [(≡SiO-<i>ⁱ</i>^Pr4PCP)Ir(CO)] (<b>2</b>) were synthesized via immobilization of molecular precursors. These complexes were used for gas-phase butane transfer dehydrogenation using increasingly sterically demanding olefins, resulting in observed selectivities of up to 77%. The results indicate that the active site is conserved upon immobilization.

Regioselective Gas-Phase n-Butane Transfer Dehydrogenation via Silica-Supported Pincer-Iridium Complexes

<b>Abstract:</b> The production of olefins via on-purpose dehydrogenation of alkanes allows for a more efficient, selective and lower cost alternative to processes such as steam cracking. Silica-supported pincer-iridium complexes of the form [(≡SiO-^R4POCOP)Ir(CO)] (^R4POCOP = κ³-C₆H₃-2,6-(OPR₂)₂) are effective for acceptorless alkane dehydrogenation, and have been shown stable up to 300 °C. However, while solution-phase analogues of such species have demonstrated high regioselectivity for terminal olefin production under transfer dehydrogenation conditions at or below 240 °C, in open systems at 300 °C, regioselectivity under acceptorless dehydrogenation conditions is consistently low. In this work, complexes <a>[(≡SiO-<i>^t</i>^Bu4POCOP)Ir(CO)] </a>(<b>1</b>) and [(≡SiO-<i>ⁱ</i>^Pr4PCP)Ir(CO)] (<b>2</b>) were synthesized via immobilization of molecular precursors. These complexes were used for gas-phase butane transfer dehydrogenation using increasingly sterically demanding olefins, resulting in observed selectivities of up to 77%. The results indicate that the active site is conserved upon immobilization.

A Concise and Modular Three-Step Synthesis of (S)-Verapamil using an Enantioselective Rhodium-Catalyzed Allylic Alkylation Reaction

A concise and modular asymmetric synthesis of the calcium channel blocker (S)-verapamil is described. This approach employs an enantioselective rhodium-catalyzed allylic alkylation reaction between an α-isopropyl-substituted benzylic nitrile and allyl benzoate to construct the challenging acyclic quaternary stereocenter. The terminal olefin then serves as a convenient synthetic handle for a hydroamination to introduce the phenethylamine moiety, furnishing (S)-verapamil in three steps and 55% overall yield, thus providing the most efficient synthesis of this important pharmaceutical reported to date. Furthermore, given the modular nature of the synthesis, it can be readily modified to prepare structurally related bioactive agents.

A hydrogen-bonded polymer constructed from mechanically interlocked, suit[1]ane monomers

A T-shaped 2,4,7-substituted benzimidazolium “axle” with two ester functionalities and a 24-membered crown ether “wheel” with appendages containing terminal olefin groups were threaded — axle through wheel — to form a [2]pseudorotaxane. Grubbs’ ring-closing metathesis (RCM) was then used to form a third loop and create a bicyclic cage that fully encapsulates the axle and permanently interlocks the two molecular components creating a suit[1]ane. There are no bulky groups on the axle to prevent unthreading, but the axle is trapped due to the cage-like nature of the newly created polyether host. After hydrolysis of the esters groups to carboxylic acids, this novel mechanically interlocked molecule (MIM) polymerizes in the solid state. The structure of the resulting supramolecular polymer was determined by single-crystal X-ray diffraction and contains linear one-dimensional tapes of suit[1]ane monomers linked by intermolecular hydrogen bonding between the carboxylic acid groups.

Vanadium-Catalyzed Oxidation of Terminal Olefin with Molecular Oxygen: Competing Products between Epoxide and Aldehyde

This work may give an understanding of why epoxide and aldehyde are easily generated in olefin oxidation by molecular oxygen when vanadium phenoxyimine complex was employed as a catalyst. This work would also explain why oxetane and dioxetane were harder to produce, although a radical tautomerism may allow the formation of such products.