The [2+2] cycloaddition product of perhalogenated cyclopentadienyl cations: structural characterization of salts of the [C10Cl10]2+ and [C10Br10]2+ dications

Perchlorinated and perbrominated organic dications [C10Cl10]2+ and [C10Br10]2+ have been obtained instead of monomeric cyclopentadienyl cations C5Cl5+ and C5Br5+.

Reactivity of allenylphosphonates/allenylphosphine oxides – some new addition/cycloaddition and cyclization pathways

In this paper, we highlight some addition/cycloaddition reactions of allenylphosphonates and allenylphosphine oxides, mostly based on the work done in our laboratory. Thus the electrophilic addition of iodine monochloride (ICl) with allenylphosphine oxides affords cyclic phosphonium salts rather than γ-chloro-β-iodovinylphosphine oxides (NMR, HRMS, X-ray) that exhibit rather unusual downfield shifts in the 31P NMR spectra. These compounds undergo hydrolysis to afford γ-hydroxy-β-iodovinylphosphine oxides; the hydroxymethyl group in these compounds can be oxidized by Dess-Martin periodinane to afford the corresponding aldehyde-substituted vinylphosphine oxides. A [2+2] cycloaddition product of an allenylphosphonate has also been structurally characterized. Other reactions that are highlighted include those leading to (Z)/(E)-β-aminovinylphosphonates, β-ketophosphonates (and their utility in Horner-Wadsworth-Emmons reaction), indolyl/furanyl/isocoumaranyl/naphthyl phosphine oxides, thiophosphorylated phosphonates and azo-substituted coumarin phosphonates.

Isomerism in double-pillared-layer coordination polymers – structures and photoreactivity

The existence of isomerism in coordination polymeric structures offers opportunities to understand structure–function relationships. Herein the serendipitous isolation is reported of two isomeric double-pillared-layer coordination polymeric structures arising from two different types of carboxylate bonding of benzene-1,4-dicarboxylate ligands to zinc(II), which constitutes a new type of structural isomerism. The different bonding modes not only alter the shape and size of the pores, but also the nature of interpenetration and photoreactivity. Although twotrans,cis,trans-bpeb ligands with conjugated olefin bonds are aligned in close proximity in both of the structures, one isomer undergoes a double [2 + 2] cycloaddition reaction and the second isomer only offers an incomplete single cycloaddition product. This work demonstrates how small changes in the structural connectivity can have an impact on the overall structural, physical and chemical properties of such materials.

Metal nitrene-like reactivity of a SiN bond towards CO2

The unusual reactivity of the SiN bond in metallo-iminosilane [DippN = Si(OSiMe3)Ni(Cl)(NHC)2]1towards CO2and cyclohexyl isocyanate (CyNCO) is reported;1reacts with two molar equiv. of CO2to give the [2+2+2] cycloaddition product3with complete scission of the σ- and π-Si–N bonds, akin to transition-metal nitrene complexes.

Straightforward regioselective construction of 3,4-dihydro-2H-1,4-thiazine by rhodium catalysed [3 + 3] cycloaddition of thiirane with 1-sulfonyl-1,2,3-triazole: a pronounced acid additive effect

A rhodium catalyzed regioselective coupling of thiirane with 1-sulfonyl-1,2,3-triazole has been realized to give a formal [3 + 3] cycloaddition product 3,4-dihydro-2H-1,4-thiazine via the 1,3-insertion model of azavinyl carbene.

Addition of phenylacetylene to a magnesium complex of monoiminoacenaphtheneone (dpp-mian)

Reaction of alkoxy-amido magnesium complex 4 with phenylacetylene affords cycloaddition product 6. The protonation of the latter with phenylacetylene results alkoxy-imino derivative 7.

Thiourea-catalyzed Diels–Alder reaction of a naphthoquinone monoketal dienophile

A variety of organocatalysts were screened for the catalysis of the naphthoquinone monoketal Diels–Alder reaction. In this study we found that Schreiner's thiourea catalyst 10 and Jacobson's thiourea catalyst 12 facilitate the cycloaddition of the sterically hindered naphthoquinone monoketal dienophile 3 with diene 4. The use of thiourea catalysis allowed for the first time the highly selective synthesis of the exo-product 2a in up to 63% yield. In this reaction a new quaternary center was built. The so formed cycloaddition product 2a represents the ABC tricycle of beticolin 0 (1) and is also a valuable model substrate for the total synthesis of related natural products.