FeIII Quinolylsalicylaldimine Complexes: A Rare Mixed‐Spin‐State Complex and Abrupt Spin Crossover

A new synthesis of (8‐quinolyl)‐5‐methoxysalicylaldimine (Hqsal‐5‐OMe) is reported and its crystal structure is presented. Two Fe^III complexes, [Fe(qsal‐5‐OMe)₂]Cl ? solvent (solvent=2 MeOH ? 0.5 H₂O ( 1 ) and MeCN ? H₂O ( 2 )) have been prepared and their structural, electronic and magnetic properties studied. [Fe(qsal‐5‐OMe)₂] Cl ? 2 MeOH ? 0.5 H₂O ( 1 ) exhibits rare crystallographically independent high‐spin and low‐spin Fe^III centres at 150 K, whereas [Fe(qsal‐5‐OMe)₂]Cl ? MeCN ? H₂O ( 2 ) is low spin at 100 K. In both structures there are extensive π–π and C? H???π interactions. SQUID magnetometry of 2 reveals an unusual abrupt stepped‐spin crossover with T_1/2=245 K and 275 K for steps 1 and 2, respectively, with a slight hysteresis of 5 K in the first step and a plateau of 15 K between the steps. In contrast, 1 is found to undergo an abrupt half‐spin crossover also with a hysteresis of 10 K. The two compounds are the first Fe^III complexes of a substituted qsal ligand to exhibit abrupt spin crossover. These conclusions are supported by ⁵⁷Fe Mössbauer spectroscopy. Both complexes exhibit reversible reduction to Fe^II at ?0.18 V and irreversible oxidation of the coordinated qsal‐5‐OMe ligand at +1.10 V.     

Radical Cyclization/ipso‐1,4‐Aryl Migration Cascade: Asymmetric Synthesis of 3,3‐Difluoro‐2‐propanoylbicyclo[3.3.0]octanes

A novel method for the asymmetric synthesis of 3,3‐difluoro‐2‐propanoylbicyclo‐[3.3.0]octanes involves an unprecedented intramolecular radical cyclization/ipso‐1,4‐aryl migration cascade.     

The Morita?Baylis?Hillman Reaction of Chiral Highly Oxygenated Cyclopent‐2‐enones

The Morita? Baylis? Hillman (MBH) reactions of (4S,5R,7R,8R)‐ and (4R,5R,7R,8R)‐4‐hydroxy‐7,8‐dimethoxy‐7,8‐dimethyl‐6,9‐dioxaspiro[4.5]dec‐2‐en‐1‐ones ( 2 and 3 , resp.) with aldehydes using various catalysts were studied. A combination of Bu₃P/phenol in THF was found being optimum conditions giving the corresponding MBH adducts with high diastereoisomeric ratios. After separation, each stereomerically pure isomer of the MBH adducts was subjected to hydrolysis employing 1% aq. CF₃COOH (TFA) in a water bath of an ultrasonic cleaner to afford the corresponding polyhydroxylated cyclopentenones in good yields.     

Enantioselective synthesis of alpha-ionone derivatives using an anti S(N)2' substitution of functionalized zinc organometallics

[reaction: see text] The allylic substitution of sterically hindered (2-iodocycloalkyl)phosphates proceeds with complete anti S(N)2' stereoselectivity with mixed diorganozincs of the type RZnCH(2)SiMe(3) in the presence of CuCN.2LiCl. Only the group R of the copper-zinc reagent is transferred in the allylic substitution. This method was used to prepare odoriferous substances such as (R)-alpha-ionone in 97% ee and (R)-dihydro-alpha-ionone in 98% ee.     

Synthesis of gem-difluoromethylenated bicyclo[m.n.0]alkan-1-ols and their ring-expansion to gem-difluoromethylenated macrocyclic lactones

Fluoride-catalyzed stereoselective nucleophilic addition of PhSCF(2)SiMe(3) (1) to α-carboethoxycycloalkanones 2 followed by intramolecular radical cyclization of the resulting cis-3 adduct afforded the corresponding gem-difluoromethylenated bicyclic compounds 4, which underwent ring-expansion followed by the Baeyer-Villiger-type oxidation of the resulting macrocyclic ketone intermediates to give gem-difluoromethylenated macrocyclic lactones 5.     

Stereoselective S N 2-substitutions using polyfunctional lithium arylcuprates prepared by an iodine-copper exchange

[reaction: see text] Polyfunctional mixed lithium arylcuprates of the type (FG-Ar)(PhMe(2)CCH(2))CuLi obtained via iodine- or bromine-copper exchange with (PhMe(2)CCH(2))(2)CuLi react with cyclic 2-iodoallylic acetates with high S(N)2 selectivity. The addition of ZnBr(2) changes this selectivity and allows the performance of highly regioselective and enantioselective anti S(N)2' substitutions using open-chain allylic pentafluorobenzoates.     

Highly diastereoselective alkylation of vicinal dianions of chiral succinic acid derivatives: a new general strategy to (R)-β-arylmethyl-γ-butyrolactones

The vicinal dianions derived from chiral succinic acid derivatives, 1,4-bis[(4R,5S)-3,4-dimethyl-2-oxo-5-phenylimidazolidin-1-yl]butane-1,4-dione and 1,4-bis[(4S,5R)-3,4-dimethyl-2-oxo-5-phenylimidazolidin-1-yl]butane-1,4-dione react with arylmethyl bromides with high diastereo- and regio-selectivity to provide the corresponding chiral α-arylmethylated succinic acid derivatives; the (R)-products are converted into (R)-β-arylmethyl-γ-butyrolactones and (R)-α-arylmethyl-γ-butyrolactones.     

Effect of the β-diketonate ligand on the spin states of [Ni(β-dkt)2(NH2-quin)] complexes

Three new complexes [Ni(β-dkt)₂(NH₂-quin)] {β-dkt = 2,2,6,6-tetramethylheptane-3,3-dionate (tmhd) 1, hexafluoroacetylacetonate (hfac) 2, 1,3-diphenylpropanedionate (dbm) 3} have been prepared by reacting [Ni(β-dkt)₂(H₂O)₂] with 8-aminoquinoline (NH₂-quin). [Ni(tmhd)₂(NH₂-quin)] is found to be solvatochromic exhibiting a square planar geometry in CH₂Cl₂, acetone, and acetonitrile with the tmhd ligand acting unusually as a counteranion while in THF and DMSO the complex is octahedral. In contrast, 2 and 3 are octahedral in all solvents. Single crystal X-ray diffraction studies reveal octahedral nickel centres with a cis arrangement of the β-diketonates. The molecular packing consists of hydrogen bonded dimers which in the case of 2 and 3 are connected to one another via π···π and C-H?π interactions, respectively. Cyclic voltammetry shows 1 and 3 oxidise irreversibly at 0.46 and 1.17 V, respectively.