Enumerating rc-Invariant Permutations with No Long Decreasing Subsequences

We use the Robinson-Schensted-Knuth correspondence and Schützenberger’s evacuation of standard tableaux to enumerate permutations and involutions which are invariant under the reverse-complement map and which have no decreasing subsequences of length k. These enumerations are in terms of numbers of permutations with no decreasing subsequences of length approximately frack2;{{frac{k}{2}};} we use known results concerning these quantities to give explicit formulas when k ≤ 6.     

Molecular Turnstiles Featuring Bicyclic Rotators: Solution and Solid-State Investigation of Steric and Electronic Concerns

A molecular rotor is created when a 2,1,3-benzothiadiazole rotator is incorporated into a rigid arylene ethynylene framework supported by pyridine coordination to a metal (Ag⁺ or PdCl₂) guest. Comparisons to a similarly sized naphthyl rotator via ¹H NMR spectroscopy provide insights into the movement of these bicyclic rotators relative to the rigid stator framework. Chemical shift increases of 0.3 ppm, or more, upon metal complexation are consistent with through-space interaction of the central arene with a bound PdCl₂ guest. Further study via X-ray crystallography illustrates that rotation of the 2,1,3-benzothiadiazole unit in the solid state is likely hampered by relatively strong chalcogen bonding (N⋅⋅⋅S distance of 2.93 Å), forming 2S-2N squares between benzothiadiazoles of neighboring complexes. Strong π–π interactions (3.29–3.36 Å) between neighboring complexes likewise restrict solid-state rotation of the potential benzothiadiazole rotator. Modest changes to UV–vis spectra upon metal coordination suggest that electronic properties are mostly independent of stator configuration.     

Atypical “Masked” Frustrated Lewis Pair Character in a Geminal-Linked Phosphine-Borane

We report the synthesis and reactivity of the geminal-linked fluorene-derived P/B frustrated Lewis pair (FLP) ⁱPr₂P(C₁₃H₈)BCy₂ ( 1 ). Compound 1 displays anomalous behavior towards small molecules, acting as a “masked” FLP. This behavior stems from significant polarization of the B−C(fluorene) bond in 1 , as identified by density functional theory (DFT) computations. We exploit this B−C bond polarity through reactions with PhPCl₂, H₃N ⋅ BH₃, and ⁱPrNH₂, demonstrating P−Cl and N−H bond activation, respectively.     

Quantitative Determination of Water in Organic Liquids by Ambient Mass Spectrometry

This study uses a rapid tandem mass-spectrometry method to determine water content in complex organic solutions. Emphasis is placed on trace-water analysis by a fast and accurate alternative to the Karl–Fischer method. In this new method, water is captured by a charge-labeled molecular probe. Water binds strongly with high specificity to the strongly electrophilic aldehyde site in a charge-labelled molecule (N-methylpyridinium); competitive binding by other analytes is effectively discriminated against in the mass-measurement step. Quantitative determinations are made over a wide concentration range, 0.001 % (10 ppm) to 99 %, with better than 10 % relative standard deviation, along with short (1 min) analysis times using small sample volumes (several μL). Applications include water measurement in simple organic solvents, for example, deuterated solvents, as well as in complex mixtures, for example, organic reaction mixtures. Additionally, this method allows for water monitoring in levitated droplets. Mechanistic investigations into the impact of water on important chemical processes in organic synthesis and environmental science are reported.     

Asymmetric synthesis of all-carbon benzylic quaternary stereocenters via Cu-catalyzed conjugate addition of dialkylzinc reagents to 5-(1-arylalkylidene) Meldrum's acids

The asymmetric synthesis of all-carbon benzylic quaternary stereocenters has been successfully achieved through copper-catalyzed addition of dialkylzinc reagents to 5-(1-arylalkylidene) and 5-(dihydroindenylidene) Meldrum's acids in the presence of phosphoramidite ligand. The resulting benzyl-substituted Meldrum's acids and 1,1-disubstituted indanes were obtained in good yields and up to 99% ee. The significance of substituting the position para, meta, and ortho to the electrophilic benzylic center was highlighted. A benzyl Meldrum's acid product was further transformed to a 3,3-disubstituted 1-indanone and a beta,beta-disubstituted pentanoic acid.     

Synthesis of daunorubicin analogues containing truncated aromatic cores and unnatural monosaccharide residues

The anthracycline antibiotics daunorubicin and doxorubicin have been used widely as anticancer drugs, but their cardiotoxicity limits their clinical use. We describe here the preparation of a small panel of daunorubicin analogues in which the anthraquinone core is replaced with simpler aromatic moieties that lack a quinone functionality. The targets consist of a functionalized 1,2,3,4-tetrahydro-naphthalene or 1,2,3,4-tetrahydro-anthracene core bound to one of three monosaccharides: daunosamine, acosamine, or 4-amino-2,3,6-trideoxy-l-threo-hexopyranose. Key steps in the synthesis included an enantioselective ring opening of benzo-fused norbornene derivatives for the preparation of the core structures and the use of silver hexafluorophosphate-promoted thioglycoside activation in the glycosylation of these cores. Evaluation of these compounds against the MCF-7 cancer cell line demonstrated that the identity of the carbohydrate moiety appeared to have little influence on the cytotoxicity. Moreover, the analogues with the 1,2,3,4-tetrahydro-naphthalene core showed no cytotoxicity, while those possessing the 1,2,3,4-tetrahydro-anthracene moiety were more active. The IC50 values for the latter group of compounds were in the range of 94-134 microM, compared to 17 microM for doxorubicin and 5 microM for daunorubicin.     

Editorial 70 (the platinum issue)

Foundations of Chemistry -