Intra- and intermolecular trapping of cyclopentapyrazine carbenes derived from 1,2-dialkynylimidazoles

The thermolysis of 1,2-dialkynylimidazoles in benzene solution affords high yields of 7-phenyl-5H-cyclopentapyrazines, which presumably form by solvent trapping of cyclopentapyrazine carbene intermediates. In cases where dialkynylimidazole contains side chains that can participate in intramolecular carbene C-H insertion or olefin addition, these processes compete with solvent addition to afford novel tri- and tetracyclic pyrazines, which can be obtained in good yield when the thermolysis is carried out in hexafluorobenzene.     

Domino carbocationic rearrangements of α-[bis(methylthio)methylene]alkyl-2-(heteroaryl)cyclopropyl ketones

Domino carbocationic rearrangements of α-[bis(methylthio)methylene]alkyl-2-(heteroaryl)cyclopropyl ketones (X=O, S, NMe) bearing five-membered heteroaryl group have been investigated. Although the cyclopropyl ketones (R¹=H) gave similar products like their aryl counterparts under these conditions, the corresponding α-methylcyclopropyl ketones (R¹=Me) yielded a variety of unexpected products depending on the nature of heteroaryl group in the substrate cyclopropyl ketones and the type of acid catalyst used. A probable mechanism for the formation of various products in these transformations has been proposed.     

Chemo- and regioselective synthesis of 2-alkylidenetetrahydrofurans bearing a chiral sulfur atom by domino reactions of sulfoximines

The addition of the dianion of Johnson’s sulfoximine to α,ω-halogenoesters evolves by an intramolecular heterocyclization to provide a direct access to 2-alkylidenetetrahydrofurans bearing a chiral sulfur atom via domino addition-elimination/S_N reactions.     

取代1,1'-联-2-萘酚在铜胺络合物催化作用下的氧化反应

用CuCl2?2H2O与小分子的有机胺形成络合物,模拟氧化还原酶对多米诺式反应(Dominoreaction)进行催化反应,在氧气存在条件下,取代1,1'-联-2-萘酚化合物被氧化为二苯并呫吨类化合物,产物的结构经核磁共振、红外光谱及质谱进行确证.     

Double domino Knoevenagel hetero Diels-Alder strategy towards bis-pyrano-1,4-benzoquinones

Several bis-pyrano-l,4-benzoquinones have been synthesized by a double domino Knoevenagel hetero Diels-Alder reaction. The synthetic approach is highly efficient allowing the construction of complex polycyclic scaffolds with six new σ-bonds. These reactions performed more efficiently and more rapidly using microwave irradiation. The resulting bis-pyrano-1,4-benzoquinones are the first examples of a double domino Knoevenagel hetero Diels-Alder reaction. Our approach represents a novel contribution to the chemistry of 2,5-dihydroxy-l,4-benzoquinones and the first general method for the synthesis of bis-pyranobenzoquinones.     

Domino allylation and cyclization of ortho-alkynylbenzaldehydes with allyltrimethylsilane catalyzed by Pd(II)-Cu(II) bimetallic systems

The reaction of ortho-alkynylated benzaldehydes 1 with allyltrimethylsilane under the Pd(OAc)₂-CuCl₂ catalyst system gave the isochromene derivatives 2 together with the chlorinated products 3. When the reaction was conducted in the presence of half equiv of H₂O, the formation of 3 was suppressed and 2 was obtained in good to high yields. When the reaction of 1a was carried out with trimethylsilylcyanide instead of allylsilane, the cyano group-substituted isochromene 9 was obtained in 94% yield.     

Palladium catalyzed domino C-H activation strategy: An access to 9- fluorenones

Palladium catalyzed domino C-H functionalization reaction of arylaldehyde with dihaloarene has been developed to access 9-flourenone molecules. Bidentate ligand assisted strategy, single step reaction, high yield and excellent functional group tolerance make this method concise and effective for the synthesis of 9-flourenone. In addition, proposed method has been successfully employed to synthesise Tilorone in gram scale.     

APICOPHILICITY AND RING-STRAIN IN FIVE-COORDINATE PHOSPHORANES

Abstract

In order to dicuss mechanism in organophosphorus chemistry a number of assumptions have to be made. Among them are: (a) that substitutions at tetrahedral phosphorus proceed via five-coordinate intermediates; (b) these intermediates are trigonal bipyramidal; (c) they are formed by apical attack and decompose by apical loss; and (d) if sufficiently long-lived, they may undergo permutational isomerization, that is the ligands may alter their relative dispositions round the phosphorus, before going on to products or back to reactants.

Assuming that the course of a given substitution is dictated primarily by thermodynamic considerations, in order to understand the course of that substitution one needs to know how to assess the relative stabilities of the four isomeric tbps (trigonal bipyramids) that can be formed initially and of the others that could be formed by subsequent isomerization, the barriers to those isomerizations, and the relative rates of the various product-forming steps. We have concentrated on the first of these factors and this lecture describes our attempts to provide the necessary data.

The energy difference between two isomeric tbps can be analyzed in terms of changes in the relative apicophilicities¹ of the groups occupying apical positions, changes in ring-strain as small rings move between apical-equatorial and diequatorial positions, and changes in steric strain. I shall consider each of these in turn. Ligand subset symmetry may also have to be taken into account.^1,2     

Alternate Method for the Synthesis of Six-Membered Carbocycles with Five Stereocenters: 1,2,3,4,6-Pentasubstituted-4-hydroxy-cyclohexanes

A series of novel 1,2,3,4,6-pentasubstituted-4-hydroxy-cyclohexanes (3a–u) were synthesized from the reaction of aromatic ketones with aromatic aldehydes under mild reaction conditions in good yields. The stereochemistry of the synthesized compounds was established using 1D and 2D-NMR spectra.     

Domino reactions in water for the stereoselective synthesis of novel spiro dihydro-2′H-[indene-2,3′-thiophen]-1(3H)-ones with three contiguous stereocenters

The domino reactions of (E)-2-(aryl)-2,3-dihydro-1H-inden-1-ones and 1,4-dithiane-2,5-diol in the presence of triethylamine in water stereoselectively afforded a library of 2′-(aryl)-4′-hydroxy-4′,5′-dihydro-2′H-spiro[indene-2,3′-thiophen]-1(3H)-ones. This transformation presumably proceeds via the generation of 2-mercaptoacetaldehyde from 1,4-dithiane-2,5-diol followed by Michael addition–intramolecular aldol sequence with C–C and C–S bond formations and creation of three contiguous stereocenters in a one-pot operation.