Simple and efficient synthesis of thysanone methyl ether

The synthesis of thysanone methyl ether is achieved by employing semivioxanthin methyl ether, which in turn is prepared by the tandem Michael addition of an anion of orsellinate to a substituted dihydropyrone.     

Addition of selenium dibromide to divinyl sulfide: spontaneous rearrangement of 2,6-dibromo-1,4-thiaselenane to 5-bromo-2-bromomethyl-1,3-thiaselenolane

Synthesis of the novel selenium heterocycles 1, 2, and 3 based on the addition reaction of selenium dibromide to divinyl sulfide is described. The reaction proceeded in CCl₄ at room temperature to give the thiaselenane 1. Even at low temperature in chloroform solution, the 6-membered thiaselenane 1 underwent spontaneous rearrangement to the 5-membered thiaselenolane 2. In turn, the thiaselenolane 2 underwent spontaneous dehydrobromination to the thiaselenole 3 in chloroform.     

The unique regioselectivity in the formation of disubstituted-1,4-benzoquinones generated from the reaction of 4-hydroxycoumarins with 1,4-benzoquinone

The 2,3-disubstituted 1,4-benzoquinones were synthesized through the regioselective addition of 4-hydroxycoumarins with 1,4-benzoquinone in aqueous acetone, which were different from 2,5-disubstituted adducts generated by the previously reported reaction of compounds possessing an activated methylene with 1,4-benzoquinone.     

Asymmetric anionic polymerization of 2,6-dimethyl-7-phenyl-1,4-benzoquinone methide

Asymmetric anionic polymerizations of 2,6-dimethyl-7-phenyl-1,4-benzoquinone methide ( 1 ) were performed with various chiral anionic initiators, and the specific rotations of the obtained polymers were investigated. Optically active poly( 1 )s with configurational chirality were obtained with all the initiators, and a complex of fluorenyllithium (FlLi) with (−)-sparteine [(−)-Sp] produced poly( 1 ) with the largest negative specific rotation ([α]₄₃₅ = −26.8°). The specific rotations of poly( 1 )s obtained with FlLi/(−)-Sp depended on the initiator concentration and the solvent polarity. The maximum specific rotations were obtained at an almost constant initiator concentration (ca. 0.03 mol/L), regardless of the monomer concentration, in toluene, whereas a higher initiator concentration was required in more polar solvents. These results suggested that the aggregation state of the propagating chain end significantly affected the specific rotation of poly( 1 ). © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4548–4555, 2004     

Microwave-assisted combined Mitsunobu reaction-Claisen rearrangement and microwave-assisted phenol oxidation: rapid synthesis of 2,6-disubstituted-1,4-benzoquinone natural products

Microwave irradiation of a phenol, an allylic alcohol, di-isopropyl azodicarboxylate and triphenylphosphine at 220-240 °C for 30 min results in a combined Mitsunobu reaction and Claisen rearrangement to give the rearranged 2-allylphenol. Following the first detailed study of microwave-assisted phenol oxidation, rapid syntheses of the natural products primin and 2-methoxy-6-pentadecyl-1,4-benzoquinone (four reaction steps, total reaction time 1 h) were achieved using this combined Mitsunobu-Claisen strategy in combination with two further microwave-assisted steps (alkene hydrogenation and phenol oxidation).     

Characteristics of Triplet Exciplexes in the Photolysis of 2,6-Diphenyl-1,4-benzoquinone with Amines

Russian Journal of Physical Chemistry A - The spectral and kinetic characteristics of short-lived triplet exciplexes, formed by quenching the triplet state of acceptor 2,6-diphenyl-1,4-benzoquione...     

Organocatalytic Asymmetric 1,6‐Addition/1,4‐Addition Sequence to 2,4‐Dienals for the Synthesis of Chiral Chromans

A novel asymmetric organocatalytic 1,6‐addition/1,4‐addition sequence to 2,4‐dienals is described. Based on a 1,6‐Friedel–Crafts/1,4‐oxa‐Michael cascade, the organocatalyst directs the reaction of hydroxyarenes with a vinylogous iminium‐ion intermediate to give only one out of four possible regioisomers, thus providing optically active chromans in high yields and 94–99 % ee. Furthermore, several transformations are presented, including the formation of an optically active macrocyclic lactam. Finally, the mechanism for the novel reaction is discussed based on computational studies.     

Studies on Quinones. XIX. Improved Synthesis of 2-Nitro-1,4-benzoquinone and its Reaction with Nucleophiles

Reaction of 2-nitro-1,4-benzoquinone (4), easily obtained by oxidation of 3 with MnO₂/HNO₃, with various nucleophiles affords the corresponding adducts in high yields.     

Stereoselective synthesis of highly oxygenated cyclohexanes through a [3+3] annulation approach

The synthesis of highly oxygenated cyclohexanes has been achieved through a Michael–Wittig protocol via a [3+3] annulation of the enal that is derived from 2,3-O-isopropylidene-(R)-glyceraldehyde. The γ-alkoxy enal system is responsible for the stereoselectivity.     

1,4‐Addition of TMSCCl3 to Nitroalkenes: Efficient Reaction Conditions and Mechanistic Understanding

Improved synthetic conditions allow preparation of TMSCCl₃ in good yield (70 %) and excellent purity. Compounds of the type NBu₄X [X=Ph₃SiF₂ (TBAT), F (tetrabutylammonium fluoride, TBAF), OAc, Cl and Br] act as catalytic promoters for 1,4‐additions to a range of cyclic and acyclic nitroalkenes, in THF at 0–25 °C, typically in moderate to excellent yields (37–95 %). TBAT is the most effective promoter and bromide the least effective. Multinuclear NMR studies (¹H, ¹⁹F, ¹³C and ²⁹Si) under anaerobic conditions indicate that addition of TMSCCl₃ to TBAT (both 0.13 M ) at ?20 °C, in the absence of nitroalkene, leads immediately to mixtures of Me₃SiF, Ph₃SiF and NBu₄CCl₃. The latter is stable to at least 0 °C and does not add nitroalkene from ?20 to 0 °C, even after extended periods. Nitroalkene, in the presence of TMSCCl₃ (both 0.13 M at ?20 °C), when treated with TBAT, leads to immediate formation of the 1,4‐addition product, suggesting the reaction proceeds via a transient [Me₃Si(alkene)CCl₃] species, in which (alkene) indicates an Si???O coordinated nitroalkene. The anaerobic catalytic chain is propagated through the kinetic nitronate anion resulting from 1,4 CCl₃^? addition to the nitroalkene. This is demonstrated by the fact that isolated NBu₄[CH₂?NO₂] is an efficient promoter. Use of H₂C?CH(CH₂)₂CH?CHNO₂ in air affords radical‐derived bicyclic products arising from aerobic oxidation.     

Highly Enantioselective 1,4‐Addition of Diethyl Phosphite to Enones Using a Dinuclear Zn Catalyst

Zinc benefits : The first catalytic asymmetric phospha‐Michael addition of enones has been developed. Under mild reaction conditions, the γ‐oxo phosphonates could be obtained in high yields (up to 99 %) with excellent enantioselectivities (93–99 % ee; see scheme). The strategy makes the asymmetric synthesis of biologically important phosphonate compounds more accessible.

     

亚甲基丙二酸亚异丙酯衍生物的氰化加成

对5-位不饱和双键的氰化加成进行了研究,合成了一系列新的5-氰基甲基丙二酸亚异丙酯的衍生物.