Parahydrogen studies of H2 addition to Ir(I) complexes containing chiral phosphine-thioether ligands: implications for catalysis

Ir(CO)[CpFe{eta5-C5H3(PPh2)CH2SR}]Cl [R = Ph and (t)Bu], containing a kappa2:P,S ligand, undergoes H2 addition across the S-Ir-CO axis under kinetic control to form two distinct diastereoisomeric products, which then rearrange via S dissociation in a process that can be hijacked for useful catalysis, but ultimately form a single diastereoisomer of the thermodynamic product where the hydride ligands are trans to chloride and phosphine.     

Sequestered alkyllithiums: why phenyllithium alone is suitable for betaine-ylide generation

The key step in the trans-selective modification of the Wittig reaction is the alpha-lithiation of the lithium bromide coordinated ylide-aldehyde adduct (the so-called "P-betaine"). Only phenyllithium effects this deprotonation rapidly and cleanly. Alkyllithiums (in particular, butyl-, sec-butyl-, and tert-butyllithium) react only sluggishly and incompletely, being tied up in very stable mixed aggregates with the lithium alkoxide part of the betaines.     

Poly(ruthenium carbonyl spirobifluorenylporphyrin): a new polymer used as a catalytic device for carbene transfer

Oxidative electropolymerization of tetraspirobifluorenyl porphyrin ruthenium(II) carbonyl complexes can be used to coat Pt electrodes with polymeric films; after being removed from the electrode, these polymeric materials are able to catalyze the heterogeneous cyclopropanations and 2,3 sigmatropic rearrangements with ethyl diazoacetate.     

Polar Substituent Effects in the Solvolysis of Acyclic Tertiary Chlorides Polar Effects VI

The influence of twenty substituents R on the solvolysis rates and products of tertiary chlorides R - CH₂CH₂C(CH₃)₂Cl (7) has been studied. H, CH₃, (CH₃)₂NCH₂, ClCH₂, Cl, CN and NO₂ exert an inductive effect only, as the good correlation of the rates with the corresponding inductive substituent constants σ shows. Bulkier alkyl groups, i.e. isopropyl and t-butyl, lower the rate due to a Baker-Nathan effect, while the n-electron donors CH₃S, CH₃O, HO and (CH₃)₂N and the σ-electron donors (CH₃)₃Sn and HOCH₂ cause rate increases based on σ constants. These accelerations are attributed to C,C-hyperconjugative and inductomeric effects which arise in the transition state for ionization. A comparison of the reactivity of the acyclic chlorides 7 and the corresponding 1-R-substituted 3-bromoadamantanes 1a shows that polar substituent effects are more strongly transmitted in the rigid bicyclic compounds 1a than in the flexible acyclic compounds 7.     

Norbornanes. Part 18. Inductive Charge Dispersal in the Solvolyses of 4- and 5-Substituted 2-Norbornyl p-Toluenesulfonates

The solvolysis rates and products of 4- and 5-exo-substituted 2-exo- and 2-endo-norbornyl tosylates 9 and 10 , respectively, are reported. The logarithms of the rate constants (log k) correlate linearly with the inductive constants σ for the substituents. A comparison of the reaction constants p₁ for the 4-, 5-, 6-, and 7-substituted 2-exo- and 2-endo-tosylates 9 , 10 , 1 , and 2 respectively, indicates that inductivity is higher for 2-exo-ionization than for 2-endo-ionization in all series. This observation is attributed to the more favorable alignment of neighbouring C-atoms for dorsal participation in exo-ionization, especially, in the case of C(6).     

Liquid‐Crystalline Mixed [5 : 1]Hexa‐adducts of [60]Fullerene. Preliminary Communication

A liquid‐crystalline mixed [5 : 1]hexa‐adduct of [60]fullerene was synthesized by addition of two different malonate derivatives onto C₆₀. The hexa‐adduct derivative 2 was prepared by a stepwise synthetic procedure (fullerene→mono‐adduct of C₆₀→hexa‐adduct of C₆₀). Cyanobiphenyl and octyloxybiphenyl derivatives were selected as mesogens. The malonate derivatives showed either a monotropic nematic phase or a monotropic smectic A phase, and the hexa‐adduct derivative gave rise to an enantiotropic smectic A phase.     

New heterocyclic syntheses from hydrazidoyl halides. Convenient syntheses of fused pyrimidines,pyridazines, and quinazolines

Aminocyanopyrazole derivatives and pyrazolo[2,3-a]quinazolones were obtained in good yields from hydrazidoyl halides and malononitrile. Pyrazolo[3,4-d]pyridazine and pyridazo[4′,5′: 1,2]pyrazolo[1,5-a]quinazoline derivatives were synthesized in quantitative yields by reaction of hydrazine hydrate with 2 and 16 , respectively. A novel ring system, a 3-substituted tetrahydro derivative of 7-oxo-6H,8H-pyridazo[3′,4′,5′-c'd']-pyrazolo[3,4-d]pyrimidine was prepared by reaction of 6 with dimethyl carbonate. Pyrazolo[3,4-d]pyrimidine-4,6-dithiones were obtained in good yields by reaction of 2 with carbon disulfide. The structures of the products were assigned and confirmed on the basis of their elemental analyses, spectral data, and alternate synthesis wherever possible. The structures of the parent fused heterocyclic systems discussed in this work are summarized in Scheme 1 .     

Nucleophilicity and Basicity in the Quaternization of 4-Substituted Quinuclidines. Polar effects. Part III

The second order rate constants (k) for quaternization of thirty 4-substituted quinuclidines ( 1 ) by methyl iodide in methanol have been measured. The effects of the substituents on rate are relatively small and indicate an early transition state with little charge separation. They also indicate less involvement of the nitrogen atom, i.e. a looser transition state, for quaternization by allyl halides than for the less reactive propyl halides. The log k values of 4-substituted quinuclidines correlate moderately well with their pK_a values, the main reason being the imperfect correlation between nucleophilicity and basicity. The assumption that substituents exert equal effects on rates and equilibria is therefore only partly justified. Certain irregularities in the correlation can be attributed to a reduction of the nucleophilicity of nitrogen in 1 due to hydrogen bonding to the solvent methanol. Furthermore, quaternization is faster and responds more strongly to substituent effects in the aprotic solvent acetonitrile.     

Synthesis of regiospecifically polysubstituted pyridazinones

Desymmetrization of pyridazine-3,6-diones by the use of N-benzyl protective groups leads to useful starting materials for building polysubstituted pyridazine libraries in a regioselective manner.