The proton‐transfer compounds of strychnine with achiral salicylic acids: strychninium 3,5‐dinitro­salicylate and the strychninium 5‐nitro­salicylate bis­(5‐nitro­salicylic acid) adduct

In the crystal structures of the proton‐transfer compounds of strychnine with 3,5‐dinitro­salicylic acid, namely strychninium 3,5‐dinitro­salicylate, C₂₁H₂₃N₂O₂⁺·C₇H₃N₂O₇⁻, (I), and 5‐nitro­salicylic acid, namely strychninium–5‐nitro­salicylate–5‐nitro­salicylic acid (1/1/2), C₂₁H₂₃N₂O₂⁺·C₇H₄NO₅⁻·2C₇H₅NO₅, (II), protonation of one of the N atoms of the strychnine mol­ecule occurs and this group is subsequently involved in inter­molecular hydrogen‐bonding inter­actions. In (I), this is four‐centred, the primary being with an adjacent strychninium carbonyl O‐atom acceptor in a side‐to‐side inter­action giving linear chains. Other inter­actions are with the phenolate and nitro O‐atom acceptors of the anionic species, resulting in a one‐dimensional polymer structure. In (II), the N⁺—H inter­action is three‐centred, the hydrogen bonding involving carboxyl O‐atom acceptors of the anion and both acid adduct species, giving unique discrete hetero‐tetramer units. The structure of (II) also features π‐bonding inter­actions between the two acid adduct mol­ecules.     

黄钾铁矾的生物合成与鉴定

利用氧化亚铁硫杆菌的生物催化氧化作用,在FeSO4—K2SO4—H2O体系中和常温常压条件下合成赭黄色的黄钾铁矾。借助SEM,XRD,FTIR,ICP—AES等方法对它的化学组成和结构进行了分析与表征。结果表明,Thiobacillus ferrooxidans休止细胞可在2天内将FeSO4-K2SO4-H2O体系中的Fe^2 全部氧化为Fe^3 ,Fe^3 在高浓度硫酸根、K^ 存在和酸性条件下水解生成赭黄色高铁沉淀,经鉴定为黄钾铁矾,其晶体粒径均匀,分散性好,且没有无定形的羟基硫酸高铁副产物。     

Enantiomerically enriched atropisomeric N,N′-diaryl ureas by oxidative kinetic resolution of their 2-sulfanyl derivatives

Atropisomeric N-methyl-N,N′-diaryl ureas may be obtained in enantiomerically enriched form by oxidative kinetic resolution of their sulfide derivatives. The atropisomeric sulfides may be obtained in up to 97:3 er and display high stability to racemisation (half-lives at 25 °C of up to 500 years). Unlike related fully alkylated ureas, the product sulfoxides exhibit relatively weak thermodynamic conformational selectivity.     

Sample temperatures during outdoor and laboratory weathering exposures

Effective exposure temperatures (T_eff) in Arizona were calculated from hourly or 10-min parsed irradiation data along with ambient, black panel, and sample temperatures. The T_eff represents a constant temperature that creates the same amount of photodegradation as the naturally varying temperature and provides a benchmark temperature for making lifetime predictions from accelerated laboratory exposures. The annual ambient and black panel T_eff at a Wittmann, Arizona site were 30 °C and 42 °C, respectively, assuming that the photodegradation has an activation energy (E_a) of 21 kJ/mol (5 kcal/mol). T_eff was only weakly dependent on E_a over the range of 10-40 kJ/mol (3-10 kcal/mol). Samples exposed as van sunroofs were found to have T_eff that were offset from the black panel temperatures by a constant amount for the entire year. Thus, measurements of sample and black panel need to be made for only a few weeks to determine the offset and give the annual sample T_eff if the annual black panel T_eff is known. Light-colored samples probably are better compared with the ambient temperatures. Sample temperatures in xenon arc exposures usually are higher than the outdoor T_eff, so Arrhenius temperature corrections need to be carried out to relate accelerated to outdoor exposures. Temperatures in xenon arc exposure tests often correspond more closely to maximum temperatures that samples might encounter for only a few hours per year.     

Novel spiro and fused heterocycles from the allylation of indigo

The allylation of indigo results in the one-step synthesis of two unique complex heterocyclic systems: a spiroindoline-pyridoindolone arising from the addition of three allyl moieties and a fused pyridoindolo-azepinoindolone generated from the addition and subsequent cyclisation of two allyl moieties. The structures of these novel heterocycles are assigned unambiguously using extensive NMR experiments and by X-ray crystallographic analysis. The distribution of the products is influenced by the use of thermal versus microwave heating.     

One-step construction of 2-substituted-4,6-diazaindoles from carboxylic acid derivatives

Treatment of unprotected 5-amino-4-methylpyrimidine (2) with n-BuLi gave dianion 3. Direct condensation of the dianion with various carboxylic acid derivatives furnished a range of 2-substituted-4,6-diazaindoles in good yields in one step without the need for protecting groups or oxidation-state adjustment.     

Formation of water-soluble sulfonated azacalix[4]arenes from cyanuric chloride

Addition of cyanuric chloride 2 (2,4,6-trichlorotriazine) to 4,6-diaminobenzene-1,3-disulfonic acid 1 gives a bis-triazine 3 which may be cyclised with diaminoarenes to yield water-soluble azacalix[4]arenes 5a-d. Alternatively, double substitution of chloride from the bis-triazine 3 yields new bis-triazine derivatives which may likewise be cyclised to functionalised azacalixarenes bearing functionalised side chains.     

Alkyne‐Promoted H2 Loss in a Metallaborane: Nido‐to‐Closo Cluster Transformation and sp C?H Bond Oxidative Addition

A sensitive cluster : The labile rhodathiaborane [(PPh₃)₂(H)‐nido‐RhSB₉H₉(NC₅H₅)] combines the redox and coordinative flexibility of the {(PPh₃)₂(H)Rh} fragment with the capability of the 11‐vertex rhodathiaborane cluster to undergo oxidative nido‐to‐closo transformations induced by coordination of alkynes to the metal centre, which leads to hydrogenation of the triple bond, dehydrogenation of the cluster and oxidative addition of sp C? H bonds.

     

Interplay of Interactions Governing the Dynamic Conversions of Acyclic and Macrocyclic Helicates

Systemic change : A system of transformations between helical structures was observed to be governed by interactions mediated by the electronic effects of substituents, entropic effects, the conformational preferences of organic building blocks, and the coordinative preferences of the metal ion. All of these effects were important, but all must be considered together to allow the prediction of the product observed (see scheme).

     

Enantioselective Total Synthesis of Brevetoxin A: Unified Strategy for the B,E, G,and J Subunits

Brevetoxin A is a decacyclic ladder toxin that possesses 5‐, 6‐, 7‐, 8‐, and 9‐membered oxacycles, as well as 22 tetrahedral stereocenters. Herein, we describe a unified approach to the B, E, G, and J rings based upon a ring‐closing metathesis strategy from the corresponding dienes. The enolate technologies developed in our laboratory allowed access to the precursor acyclic dienes for the B, E, and G medium‐ring ethers. The strategies developed for the syntheses of these four monocycles ultimately provided multigram quantities of each of the rings, supporting our efforts toward the completion of a convergent synthesis of brevetoxin A.