The 1,4‐diacyloxylation of 1,3‐cyclohexadiene (CHD) affords valuable stereochemically defined scaffolds for natural product and pharmaceutical synthesis. Existing
The 1,4‐diacyloxylation of 1,3‐cyclohexadiene (CHD) affords valuable stereochemically defined scaffolds for natural product and pharmaceutical synthesis. Existing
- Award ID(s):
- 1953926
- NSF-PAR ID:
- 10306968
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Angewandte Chemie International Edition
- Volume:
- 60
- Issue:
- 43
- ISSN:
- 1433-7851
- Page Range / eLocation ID:
- p. 23182-23186
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
more » « less
Abstract cis ‐selective diacyloxylation protocols require superstoichiometric quantities of benzoquinone (BQ) or MnO2, which limit process sustainability and large‐scale application. In this report, reaction development and mechanistic studies are described that overcome these limitations by pairing catalytic BQ withtert ‐butyl hydroperoxide as the stoichiometric oxidant. Catalytic quantities of bromide enable a switch fromtrans tocis diastereoselectivity. A catalyst with a 1:2 Pd:Br ratio supports highcis selectivity while retaining good rate and product yield. Further studies enable replacement of BQ with hydroquinone (HQ) as a source of cocatalyst, avoiding the handling of volatile and toxic BQ in large‐scale applications. -
more » « less
Abstract The dialkyl malonate derived 1,3‐diphosphines R2C(CH2PPh2)2(R=
a , Me;b , Et;c ,n ‐Bu;d ,n ‐Dec;e , Bn;f ,p ‐tolCH2) are combined with (p ‐tol3P)2PtCl2ortrans ‐(p‐ tol3P)2Pt((C≡C)2H)2to give the chelatescis ‐(R2C(CH2PPh2)2)PtCl2(2 a –f , 94–69 %) orcis ‐(R2C(CH2PPh2)2)Pt((C≡C)2H)2(3 a –f , 97–54 %). Complexes3 a –d are also available from2 a –d and excess 1,3‐butadiyne in the presence of CuI (cat.) and excess HNEt2(87–65 %). Under similar conditions,2 and3 react to give the title compounds [(R2C(CH2PPh2)2)[Pt(C≡C)2]4(4 a –f ; 89–14 % (64 % avg)), from which ammonium salts such as the co‐product [H2NEt2]+Cl−are challenging to remove. Crystal structures of4 a ,b show skew rhombus as opposed to square Pt4geometries. The NMR and IR properties of4 a –f are similar to those of mono‐ or diplatinum model compounds. However, cyclic voltammetry gives only irreversible oxidations. As compared to mono‐platinum or Pt(C≡C)2Pt species, the UV‐visible spectra show much more intense and red‐shifted bands. Time dependent DFT calculations define the transitions and principal orbitals involved. Electrostatic potential surface maps reveal strongly negative Pt4C16cores that likely facilitate ammonium cation binding. Analogous electronic properties of Pt3C12and Pt5C20homologs and selected equilibria are explored computationally. -
more » « less
Abstract Dinuclear manganese hydride complexes of the form [Mn2(CO)8(
μ ‐H)(μ ‐PR2)] (R=Ph,1 ; R=i Pr,2 ) were used inE ‐selective alkyne semi‐hydrogenation (E ‐SASH) catalysis. Catalyst speciation studies revealed rich coordination chemistry and the complexes thus formed were isolated and in turn tested as catalysts; the results underscore the importance of dinuclearity in engendering the observedE ‐selectivity and provide insights into the nature of the active catalyst. The insertion product obtained from treating2 with (cyclopropylethynyl)benzene contains acis ‐alkenyl bridging ligand with the cyclopropyl ring being intact. Treatment of this complex with H2affords exclusivelytrans ‐(2‐cyclopropylvinyl)benzene. These results, in addition to other control experiments, indicate a non‐radical mechanism forE ‐SASH, which is highly unusual for Mn−H catalysts. The catalytically active species are virtually inactive towardscis totrans alkene isomerization indicating that theE ‐selective process is intrinsic and dinuclear complexes play a critical role. A reaction mechanism is proposed accounting for the observed reactivity which is fully consistent with a kinetic analysis of the rate limiting step and is further supported by DFT computations. -
more » « less
Abstract. We report improved synthetic routes to the isomericisoprene-derived β-epoxydiols (β-IEPOX) in high yield(57 %–69 %) from inexpensive, readily available starting compounds. Thesyntheses do not require the protection/deprotection steps or time-consumingpurification of intermediates and can readily be scaled up to yield thetarget IEPOX isomers in gram quantities. Emissions of isoprene(2-methyl-1,3-butadiene, C5H8), primarily from deciduousvegetation, constitute the largest source of nonmethane atmospherichydrocarbons. In the gas phase under low-nitric-oxide (NO) conditions,addition of the atmospheric hydroxyl radical (OH) followed by rapid addition ofO2 yields isoprene-derived hydroxyperoxyl radicals. The major sink(>90 %) for the peroxyl radicals is a sequential reaction withthe hydroperoxyl radical (HO2), OH, and O2, which is then followed bythe elimination of OH to yield a ∼2:1 mixture ofcis- and trans-(2-methyloxirane-2,3-diyl)dimethanol (cis- and trans-β-IEPOX). The IEPOXisomers account for about 80 % of closed-shell hydroxyperoxylproducts and are rapidly taken up into acidic aerosols to form secondaryorganic aerosol (SOA). IEPOX-derived SOA makes a significant masscontribution to fine particulate matter (PM2.5), which is known to be amajor factor in climate forcing as well as adversely affecting respiratory andcardiovascular systems of exposed populations. Prediction of ambientPM2.5 composition and distribution, both in regional- and global-scaleatmospheric chemistry models, crucially depends on the accuracy ofidentification and quantitation of uptake product formation. Accessibilityof authentic cis- and trans-β-IEPOX in high purity and in large quantity forlaboratory studies underpins progress in developing models as well asidentification and quantitation of PM2.5 components.
-
more » « less
Abstract MXenes are a new family of two-dimensional carbides and/or nitrides. Their 2D surfaces are typically terminated by O, OH and/or F atoms. Here we show that Ti3C2T
x —the most studied compound of the MXene family—is a good acid catalyst, thanks to the surface acid functionalities. We demonstrate this by applying Ti3C2Tx in the epoxide ring-opening reaction of styrene oxide (SO) and its isomerization in the liquid phase. Modifying the MXene surface changes the catalytic activity and selectivity. By oxidizing the surface, we succeeded in controlling the type and number of acid sites and thereby improving the yield of the mono-alkylated product to >80%. Characterisation studies show that a thin oxide layer, which forms directly on the Ti3C2Tx surface, is essential for catalysing the SO ring-opening. We hypothesize that two kinds of acid sites are responsible for this catalysis: In the MXene, strong acid sites (both Lewis and Brønsted) catalyse both the ring-opening and the isomerization reactions, while in the Mxene–TiO2composite weaker acid sites catalyse only the ring-opening reaction, increasing the selectivity to the mono-alkylated product.
