Advances in palladium catalysed wacker-type oxidative transformations

The development and optimisation of conditions for oxidative Wacker-type cyclisations followed by establishing the reaction scope are reported. Building upon the achievements in the field of oxidative Wacker-type reactions that has recently gathered interest, hydroxylamines and hydrazines were converted to isoxazolidines and pyrazolidines respectively. Secondary hydroxylamines cyclised yielding syn-isoxazolidines with excellent diastereoselectivities, whereas secondary hydrazines cyclised yielding anti-pyrazolidines but still maintained a high level of diastereoselectivity. Additionally, an enantioselective variant was explored. Isoxazolidines were successfully transformed to the corresponding 1,3-amino alcohols, which were further converted to amino sugar derivatives

Palladium-catalyzed stereoselective intramolecular oxidative amidation of alkenes in the synthesis of 1,3- and 1,4-amino alcohols and 1,3-diamines

An efficient and practical Pd-catalyzed intramolecular oxidative allylic amidation provides facile access to derivatives of 1,3- and 1,4-amino alcohols and 1,3-diamines. The method operates under mild reaction conditions (RT) with molecular oxygen (1 atm) as the sole reoxidant of Pd. Excellent diastereoselectivities were attained with substrates bearing a secondary stereogenic center Nitrogen in, hydrogen out: An efficient and practical Pd-catalyzed intramolecular oxidative allylic amidation provides facile access to derivatives of 1,3- and 1,4-amino alcohols and 1,3-diamines (see scheme). The method operates under mild reaction conditions (RT) with molecular oxygen (1 atm) as the sole reoxidant of Pd. Excellent diastereoselectivities were attained with substrates bearing a secondary stereogenic center

Vanadium(V) oxo and Imido calix[8]arene complexes: synthesis, structural studies, and ethylene homo/copolymerisation capability

Interaction of p-tert-butylcalix[8]areneH8 (L8H8) with [NaVO(OtBu)4] (formed in situ from VOCl3) afforded the complex [Na(NCMe)5][(VO)2L8H]·4 MeCN (1·4 MeCN). Increasing [NaVO(OtBu)4] to 4 equiv led to [Na(NCMe)6]2[(Na(VO)4L8)(Na(NCMe))3]2·10 MeCN (2·10 MeCN). With adventitious oxygen, reaction of 4 equiv of [VO(OtBu)3] with L8H8 afforded the alkali-metal-free complex [(VO)4L8(μ3-O)2] (3); solvates 3×3 MeCN and 3×3 CH2Cl2 were isolated. For the lithium analogue, the order of addition had to be reversed such that lithium tert-butoxide was added to L8H8 and then treated with 2 equiv of VOCl3; crystallisation afforded [(VO2)2Li6[L8](thf)2(OtBu)2(Et2O)2]·Et2O (4·Et2O). Upon extraction into acetonitrile, [Li(NCMe)4][(VO)2L8H]·8 MeCN (5·8 MeCN) was formed. Use of the imido precursors [V(NtBu)(OtBu)3] and [V(Np-tolyl)(OtBu)3] and L8H8, afforded [tBuNH3][{V(p-tolylN)}2L8H]·3 1/2 MeCN (6·3 1/2 MeCN). The molecular structures of 1 to 6 are reported. Complexes 1, 3, and 4 were screened as precatalysts for the polymerisation of ethylene in the presence of cocatalysts at various temperatures and for the copolymerisation of ethylene with propylene. Activities as high as 136 000 g (mmol(V) h)-1 were sometimes achieved; higher molecular weight polymers could be obtained versus the benchmark [VO(OEt)Cl2]. For copolymerisation, incorporation of propylene was 7.1-10.9 mol% (compare 10 mol% for [VO(OEt)Cl2]), although catalytic activities were lower than [VO(OEt)Cl2]

A Simple and Versatile Reactor for Photochemistry

A photoreactor that generates a thin film upon rotation for efficient irradiation of solutions is described. The reactor is based around a standard piece of equipment found in most synthetic laboratories, namely, a rotary evaporator. Three different photo-oxidation reactions have been used to examine the effects of several parameters such as irradiated volume, flask size, rotation speed, and light intensity. The reactor can be operated in a semicontinuous manner, and two possible configurations are described. The thickness of the generated film and the rate of mixing under different conditions have been examined using in situ electronic absorption spectroscopy

UV PhotoVap: Demonstrating How a Simple and Versatile Reactor Based on a Conventional Rotary Evaporator Can Be Used for UV Photochemistry

We report the use of a simple rotary evaporator as a semi-continuous UV photochemical reactor. By generation of a thin film from the rotation of a flask, better light penetration is achieved, and in this work we used high-power Hg lamps to enable the direct irradiation of molecules with UV light. The intramolecular [2 + 2] photocycloaddition of Cookson’s dione and the intermolecular [2 + 2] photocycloaddition of maleimide with 1-hexyne were used as test reactions to examine the effectiveness of this reactor. High productivities, equivalent to 210 g h^–1, were obtained for the simple intramolecular reaction, demonstrating the scalability of the reactor. The effects of flask size, reaction mixture volume, and use of borosilicate or quartz glassware were also investigated