The reactions of trifluoromethyl and trichloromethyl radicals with conjugated and methylene-interrupted dienes and enynes

The photochemical addition of CF₃I to buta-1,3-diene and vinylacetylene in the gas phase gave 1,4-adducts as the main products. In gas phase reactions only products derived from hydrogen abstraction were detected in the CF₃I/penta-1,3-diene system, but the 1,4-adducts again predominated in the liquid phase. CCl₃Br similarly gave a mixture of 1,2- and 1,4-adducts, the latter predominating, on photochemical reaction with penta-1,3-diene. The 1,2-adduct was the main product from the CCl₃Br/pent-1-en-4-yn reaction, but some hydrogen abstraction was observed. The preference shown by conjugated dienes to give 1,4-adducts in the $\text{trans}$- configuration is interpreted in terms of steric factors and the propensity of dienes to adopt the $\text{s}$-$\text{trans}$ conformation.     

Stereodivergent synthesis of 1,4-bifunctional compounds by regio- and diastereoselective Pd-catalyzed allylic substitution reaction

Highly stereoselective synthesis of 1,4-bifunctional compounds was accomplished via 1,2-asymmetric induction to α-oxyaldehyde and α-oxyketone followed by regio- and diastereoselective Pd-catalyzed allylic substitution reaction. We found that trifluoroacetate is a suitable leaving group for the allylic substitution reaction. Various nucleophiles containing carbon, nitrogen, and sulfur can be applied to the method. Both 1,4-syn- and 1,4-anti-adducts were synthesized with high stereoselectivity by using stereodivergent reduction of the propargyl alcohols followed by allylic substitution reaction.     

Reaction of N-arylcarbamoyl-1,4-benzoquinone imines with sodium arenesulfinates

N-Arylcarbamoyl-1,4-benzoquinone imines possessing at least one free ortho position with respect to the carbonyl carbon atom in the quinoid ring react with sodium arenesulfinates according to the nucleophilic 1,4-addition pattern with complete regioselectivity. If both ortho positions are occupied, the reaction gives a mixture of products where the major ones are 1,6- and 6,1-adducts formed according to the radical ion mechanism.     

The reaction of fluorine-containing compounds with conjugated dienoic acids initiated by sodium dithionite

The reaction of fluorine-containing halides and acetamides with conjugated dienoic acids initiated by sodium dithionite gave halide-free 1,4-adducts in 40-80% yields, with the E configuration as the major products.     

Chemoselective,accelerated and stereoselective aza-Michael addition of amines to N-phenylmaleimide by using TMEDA based receptors

An aza-Michael addition between a maleimide and amines is described in which the presence of simple amine receptors (TMEDA or trans-TMCDA) promote the chemoselectivity of the reaction (respectively, 1,2- and 1,4-addition). Additionally, both receptors are able to accelerate the reaction. Stoichiometries of complexes between receptors and amines were determined by ¹H NMR dilution experiments while enantiomeric excesses were observed on 1,4-adducts by using (1R,2R)-TMCDA.     

Reaction of a terminal phosphinidene complex with azulenes: eta1-complexes, C--H bond insertions, and 1,4-adducts

Reaction of an in situ generated phosphinidene complex [PhPW(CO)(5)] with the aromatic azulene and guaiazulene leads to unexpected 1,4-adducts of the seven-membered ring and to C--H bond insertion of the five-membered ring. A DFT analysis suggests that the reaction is initiated by formation of a eta(1)-complex between the phosphinidene and the five-membered ring of the aromatic substrate. Four conformations of this complex were identified. Two convert without barrier to the slightly more stable syn- and anti-1,2-adducts. These undergo pericyclic 1,7-sigmatropic rearrangements with remarkably low barriers to give 1,4-adducts, with an inverted configuration at the phosphorus center. An X-ray crystal structure is presented for one of the 1,4-adducts of guaiazulene. The other two eta(1)-complexes insert with modest barriers into a C--H bond of the five-membered ring.     

Regioselective 1,4-addition of nucleophiles to 1,3-diene monoepoxides catalyzed by palladium complex

1,3-Diene monoepoxides react with nucleophiles in the presence of palladium complex as a catalyst under neutral conditions to give 1,4-adducts selectively. The 1,4-adducts are allylic alcohols and there is a possibility of another nucleophilic attack. Ester of Monarch butterfly pheromone was prepared.     

Solid solution of triptycenequinone and triptycenehydroquinone as a non-stoichiometric quinhydrone. Bathochromic changes in color caused by local intermolecular interaction between p-benzoquinone and hydroquinone moieties

Binary crystal formed by 9,10-dihydro-9,10-[o]benzenoanthracene-1,4-dione (triptycenequinone, TPQ, yellow) and 9,10-dihydro-9,10-[o]benzenoanthracene-1,4-diol (triptycenehydroquinone, TPHQ, colorless) was found to be a substitutional solid solution of TPQ doped by TPHQ with concentration of TPHQ<ca. 0.2. The characteristic color (brown) of the solid solution may be ascribed to local intermolecular CT interaction between the p-benzoquinone and hydroquinone moieties of TPQ and TPHQ, respectively, enabled by a disorder in the binary crystal. It seemed appropriate to regard the solid solution as non-stoichiometric quinhydrone. Crystal structure of pure TPHQ is also reported. A common molecular arrangement in the crystals of pure TPQ and pure TPHQ, as well as the resemblance in the molecular structure, seems to be favorable for the formation of the solid solution.     

Solvent effect on the redox potential of quinone-semiquinone systems

Polarographic reduction of 1,4-benzoquinone, 1,4-naphthoquinone, 9,10-phenanthrenequinone and 9,10-anthraquinone was studied in pyridine, acetone, hexamethylphosphoramide, dimethylformamide, dimethylacetamide, acetonitrile, dimethylsulfoxide and propylene carbonate. The variation of the E_1/2-values proper for the first electron transfer step (measured against oxidation potential of ferrocene) with the properties of solvent is analyzed in terms of the donor-acceptor concept. Linear correlations of E_1/2 vs. acceptor number are observed; the slopes of corresponding lines correlate with the spin densities at oxygen atoms of semiquinones.     

Tautomeric composition and tautomeric transformation sequence of 1,4-bis(alkylamino)anthraquinones

Compounds widely known as 1,4-bis(alkylamino)-9,10-anthraquinones are in fact neither individual substances nor substituted 9,10-anthraquinones but equilibrium mixtures of tautomers. Their aminoimine tautomeric transformations follow the sequence 4,9-bis(alkylamino)-1,10-anthraquinones ? 9-alkylamino-4-(alkylimino)-10-hydroxy-1,4-dihydroanthracen-1-ones ? N ¹,N ¹⁰-dialkyl-4,9-dihydroxy-1,10-dihydroanthracene-1,10-diimines.     

1,4-Addition reaction of ethyl bromodifluoroacetate to Michael acceptors in the presence of copper powder: Improvement of the reaction using TMEDA as an additive

Reaction of ethyl bromodifluoroacetate with a variety of Michael acceptors was tremendously improved by the addition of TMEDA. Using this additive, 1,4-adducts were formed exclusively, and any 1,2-adducts or radical adducts were not obtained. THF or other low boiling solvents can be used as a solvent. This simplifies the work-up of the reaction effectively.     

Conjugated addition of cyanotrimethylsilane to α,β-unsaturated ketones

Triethylaluminium-mediated reaction of cyanotrimethylsilane with 6-methylbicyclo[4.4.0]dec-1-en-3-one affords a mixture of diastereomeric 1,4-adducts. The reaction is kinetically controlled in toluene, whereas thermodynamically in refluxing THF. 4-Methyl-3-penten-2-one and carvone analogously give the respective 1,4-adducts and a conjugated dienone addords the 1,6-adduct in good yield.     

Enantioselective copper-catalyzed 1,4-addition of dialkylzincs to enones using a novel N,N,P–Cu(II) complex

Enantioselective copper-catalyzed 1,4-additions of dialkylzincs to enones were carried out in the presence of 1 mol % of Cu(OTf)₂ and 2.5 mol % of an N,N,P-ligand possessing a tert-butyl group at the adjacent position of the nitrogen of pyridine to afford the corresponding 1,4-adducts in up to 98% ee.     

Enantioselective 1,4-Addition Reaction of α,β-Unsaturated Carboxylic Acids with Cycloalkanones Using Cooperative Chiral Amine–Boronic Acid Catalysts

An enantioselective 1,4-addition of α,β-unsaturated carboxylic acids with cycloalkanones has been developed by using chiral amine–boronic acid cooperative catalysts. In the presence of a chiral amine and boronic acid, cycloalkanones and carboxylic acids are activated as chiral enamines and mixed anhydrides, respectively. The corresponding 1,4-adducts are obtained in high yield with high enantioselectivity. Furthermore, subsequent oxylactonization of the 1,4-adducts gives spirolactones with high diastereoselectivity.     

Enantioselective conjugate addition of aliphatic thiols to divergently activated electron poor alkenes and dienes

Divergently activated double bonds in electron poor 4-oxo-butenoates and (2E,4E)-6-oxo-2,4-dienoates underwent stereoselective and regioselective addition of mercaptans catalyzed by simple Cinchona alkaloids. Application of quinine and quinidine afforded both enantiomers of the 1,4-adducts with respect to the ketone carbonyl group in ees of up to 80%. Single recrystallization of some adducts resulted in further enrichment of up to 99%ee.     

Synthesis of new bicyclic compounds containing fused sulfolane and pyrazolidine rings

3-Aryl-6а-methyl-6-nitro-1-carbamoylhexahydrothieno[2,3-d]pyrazole-4,4-dioxides, novel original bicyclic species consisting of fused pyrazolidine and sulfolane rings, and 1,4-adducts were obtained by reacting 2-benzylidene-3-methyl-4-nitro-3-thiolene-1,1-dioxide and its derivatives with semicarbazide.     

Iodine as novel reagent for the 1,2-addition of trimethylsilyl cyanide to ketones including α,β-unsaturated ketones

Molecular iodine is found to catalyze efficiently the addition of trimethylsilyl cyanide to a range of simple and functionalized ketones under very mild and convenient conditions to afford the corresponding cyanohydrin trimethylsilyl ethers in excellent yields in a short reaction period with high selectivity. α,β-Unsaturated ketones selectively afford the corresponding 1,2-adducts without the formation of 1,4-adducts under similar reaction conditions.     

N,N-dihalophosphoramides-XV: The addition of diethyl N,N-dichlorophosphoroamidate (DCPA) to conjugated 1,3-dienes

The addition of DCPA to several conjugated 1,3-dienes has been studied. The reaction was found to proceed in dichloromethane and was spontaneously or photolytically initiated depending on the structure of the dienes. N-chloro adducts, formed upon addition, could be reduced “in situ” with sodium sulphite solution to give the corresponding diethyl N-(chloroalkenyl)posphoroamidates. Addition of DCPA to terminal double bond 1,3-dienes (butadiene, isoprene and 2,3-dimethyl-1,3-butadiene) leads regiospecifically to (E)-1,4-adducts. Similarly, 1,4-addition is also observed for 1,3-cyclohexadiene. Reaction of DCPA with nonterminal double bond 1,3-dienes (trans-piperylene, 4-methyl-1,3-pentadiene, 2,5-dimethyl-2,4-hexadiene and 1,4-diphenyl-1,3-butadiene) usually affords a mixture of adducts. Spectral data and chemical transformations pertinent to the proof of structure of DCPA addition products are presented. A possible mechanism for the addition is discussed.     

The Mukaiyama-Michael addition of a β,β-dimethyl substituted silyl ketene acetal to α,β-unsaturated ketones using tetra-n-butylammonium bibenzoate as a nucleophilic catalyst

The Michael addition of a β,β-dimethyl substituted silyl ketene acetal [Me₂CC(OMe)OSiMe₃] to α,β-unsaturated ketones, namely, 2-cyclopentenone, 2-cyclohexenone, 3-methyl-2-cyclohexenone, isophorone, methyl vinyl ketone and mesityl oxide occurs smoothly in the presence of the nucleophilic catalyst, tetra-n-butyl ammonium bibenzoate (TBABB) in THF giving the corresponding 1,4-adducts in excellent yields.     

Asymmetric copper-catalyzed Diels–Alder reaction revisited: control of the structure of bis(oxazoline) ligands

Synthesis of 1,4-bis(oxazoline) ligands bearing a bicyclo[2,2,2]backbone derived from 9,10-dihydro-9,10-ethanoanthacene trans-dicarboxylic acid was revisited. Starting from l- or d-amino alcohols and either (S,S) or (R,R)-dihydroethano trans-dicarboxylic acid, a complete series of ligands was evaluated in the copper-catalyzed Diels–Alder reaction. The most efficient ligands with a phenyl substituent on the oxazoline ring afforded enantiomeric excess up to 98%. This is different from previous results indicating that the best enantioselectivity involved a diastereomeric ligand with the meso-backbone.