Further Characterization of Mitsunobu-Type Intermediates in the Reaction of Dialkyl Azodicarboxylates with P(III) Compounds

Alkylphosphinites as Synthons for Stabilized Carbocations

We present a new acid-free method for the generation of carbocations based on a redox condensation reaction that enables S_N1 reactions with a variety of nucleophiles. We utilize readily synthesized phosphinites that are activated by diisopropyl azodicarboxylate to form betaine structures that collapse upon adding a pronucleophile, thereby yielding reactive carbocation intermediates. We also employ this approach for the alkylation of some bioactive molecules.

Nitrosobenzene: Reagent for the Mitsunobu Esterification Reaction

Nitrosobenzene has been demonstrated to participate in the Mitsunobu reaction in an analogous manner to dialkyl azodicarboxylates. The protocol using nitrosobenzene and triphenylphosphine (1:1) under mild conditions (0 °C) provides the ester derivatives of aliphatic and aromatic acids using various alcohols in moderate yield and with good enantioselectivity, giving the desired products predominantly with an inversion of configuration. The proposed mechanism, which is analogous to that observed using dialkyl azodicarboxylates, involves a nitrosobenzene-triphenylphosphine adduct and an alkoxytriphenylphosphonium ion and was supported by density functional theory calculations, ³¹P NMR spectroscopy, and experiments conducted with isotopically labeled substrates.

Cocrystals of 2,6-dichloroaniline and 2,6-dichlorophenol plus three new pseudopolymorphs of their coformers

The structures of cocrystals of 2,6-dichlorophenol with 2,4-diamino-6-methyl-1,3,5-triazine, C6H4Cl2O·C4H7N5, (III), and 2,6-dichloroaniline with 2,6-diaminopyrimidin-4(3H)-one and N,N-dimethylacetamide, C6H5Cl2N·C4H6N4O·C4H9NO, (V), plus three new pseudopolymorphs of their coformers, namely 2,4-diamino-6-methyl-1,3,5-triazine-N,N-dimethylacetamide (1/1), C4H7N5·C4H9NO, (I), 2,4-diamino-6-methyl-1,3,5-triazine-N-methylpyrrolidin-2-one (1/1), C4H7N5·C5H9NO, (II), and 6-aminoisocytosine-N-methylpyrrolidin-2-one (1/1), C4H6N4O·C5H9NO, (IV), are reported. Both 2,6-dichlorophenol and 2,6-dichloroaniline are capable of forming definite synthon motifs, which usually lead to either two- or three-dimensional crystal-packing arrangements. Thus, the two isomorphous pseudopolymorphs of 2,4-diamino-6-methyl-1,3,5-triazine, i.e. (I) and (II), form a three-dimensional network, while the N-methylpyrrolidin-2-one solvate of 6-aminoisocytosine, i.e. (IV), displays two-dimensional layers. On the basis of these results, attempts to cocrystallize 2,6-dichlorophenol with 2,4-diamino-6-methyl-1,3,5-triazine, (III), and 2,6-dichloroaniline with 6-aminoisocytosine, (V), yielded two-dimensional networks, whereby in cocrystal (III) the overall structure is a consequence of the interaction between the two compounds. By comparison, cocrystal-solvate (V) is mainly built by 6-aminoisocytosine forming layers, with 2,6-dichloroaniline and the solvent molecules arranged between the layers.

Ester coupling reactions – an enduring challenge in the chemical synthesis of bioactive natural products

In this review we investigate the use of complex ester fragment couplings within natural product total syntheses. Using examples from the literature up to 2014 we illustrate the state-of-the-art as well as the challenges within this area of organic synthesis.

Quaternization and oxidation reactions of cyclodiphosphazane derivatives and their copper(I) and gold(I) complexes

The reactions of cyclodiphosphazane derivatives cis-{(t)BuN(H)P(μ-N(t)Bu)2PN(H)(t)Bu} (1), cis-{MeN(C4H8N)P(μ-N(t)Bu)2P(NC4H8Me)} (2) and {(Me2NCH2CH2O)P(μ-N(t)Bu)2P(OCH2CH2NMe2)} (3) with methyl iodide and methyl triflate and their subsequent reactions with elemental sulfur and selenium are reported. Interestingly, the reactions of 1-3 with an excess of methyl iodide resulted in quaternising only one phosphorus atom in cis-[{(t)BuNHP(μ-N(t)Bu)2P(CH3)NH(t)Bu}](I) (4), two exocyclic nitrogen atoms and one of the phosphorus atoms in cis-{(Me2NC4H8N)P(μ-N(t)Bu)2P(CH3)(NC4H8NMe2)}](I)3 (7) and only two exocyclic nitrogen atoms in cis-[{(Me3NCH2CH2O)P(μ-N(t)Bu)2P(OCH2CH2NMe3)}](I)2 (8). The reaction of 1 with one equiv. of methyl triflate produced cis-[{(t)BuN(H)P(μ-N(t)Bu)2P(CH3)N(H)(t)Bu}]OTf (5), whereas the same reaction in a 1 : 2 molar ratio afforded cis-{(t)BuN(H)P(CH3)(μ-N(t)Bu)2P(CH3)N(H)(t)Bu}(OTf)2 (6). Compounds 4 and 5 showed poor solubility in water, whereas 7 and 8 were high melting crystalline solids with moderate to good water solubility. Treatment of 4 with either elemental sulfur or selenium gave both cis- and trans-chalcogenide derivatives. Similar reactions of 7 and 8 produced both mono- and bischalcogenides. Reactions between 4 or 7 and CuI yielded dinuclear complexes, cis-[{Cu2(μ-I)3((t)BuN(H)P)(μ-N(t)Bu)2(P(CH3)N(H)(t)Bu)]2}(I)] (15) and cis-[{Cu2(μ-I)3[(Me2NC4H8N)P(μ-N(t)Bu)2P(CH3)(NC4H8NMe2)]2}(I)5] (16), while the reaction of 8 with CuI produced a coordination polymer [{Cu2(μ-I)3(μ-N(t)BuP)2(OCH2CH2NMe3)2}I]∞ (17), containing triiodo-bridged [Cu2(μ-I)3] linkers. The molecular structures of several of these compounds were confirmed by single crystal X-ray diffraction studies. The Cu(I)···Cu(I) distance of 2.55 Å in 15 is quite short and is the same as that found in copper metal and also in complexes containing [Cu2(μ-I)3] linkers. All the metal complexes exhibit strong intra-, inter- or both intra- and inter-molecular hydrogen bonding interactions.