Mark Thornton-Pett

Silver acetate catalysed cycloadditions of isocyanoacetates

Abstract Silver acetate is an efficient catalyst for the cycloaddition of methyl isocyanoacetate with Michael-acceptors under mild conditions to give Δ 1 - or Δ 2 -pyrrolines in good yields. In the case of acrolein, novel chemoselectivity was observed. In the absence of a suitable olefin isocyanoacetates undergo silver acetate catalysed cyclodimerisation to give imidazoles in excellent yields. The mechanism of the cycloadditions has been probed. The reaction has been combined with azomethine ylide 1,3-dipolar cycloadditions in a one-pot sequential cascade process to afford the 7-azabicyclo[2.2.1]heptane ring system, a characteristic structural feature of the naturally occurring potent analgesic epibatidine.

PALLADIUM CATALYSED TANDEM CYCLISATION-ANION CAPTURE PROCESSES. PART 3. ORGANOBORON ANION TRANSFER AGENTS

Abstract The cyclisation-anion capture protocol has been applied to a wide range of starter and terminating species to effect regio- and stereo-specific mono- and bis-cyclisation processes in which a variety of organoboronderivatives function as anion transfer reagents. Direct capture (no cyclisation) is rarely a problem and it can usually be suppressed by modification of the reaction conditions.

CHIRAL ALUMINIUM COMPLEXES AS PHOSPHO-TRANSFER CATALYSTS

Abstract Readily accessible, chiral complexes of aluminium are effective and enantioselective catalysts for the phospho-aldol reaction under aerobic conditions.

Synthesis of cyclometallated complexes of PdII. The X-ray crystal structure of di-μ-bromo-bis[N-(3,4-dimethoxybenzylidene)cyclohexylaminato-C6,N]dipalladium(II)

Abstract The structure of the cyclometallated bromo-brided palladium(II) dimer complex [P d{3,4-(MeO) 2 C 6 H 2 C(H)&.dbnd;N Cy}(Br)] 2 is described. This is the first example of a structurally characterised cyclometallated bromo-bridged dimer. Crystals were triclinic, space group P 1 with a = 788.7(2), b = 911.0(3), c = 1480.(4) pm, α = 96.94(2), β = 91.57(2), γ = 101.85(2)°, Z = 1, U = 1.0322(5) nm 3 , R = 0.0688, R w = 0.790, for 3280 independent reflections with F >4.0σ( F ). The structure is a centrosymmetric palladium dimer with two asymmetrically bridging bromine atoms and non-bonding Pd⋯Pd distance of 363.1(5) pm. The synthesis of the iodo-bridged analogue and the reactions of these two dimers and the chloro-bridged analogue with various tertiary phosphines are also described.

Ten-vertex metallaborane chemistry. Aspects of the iridadecaborane closo→isonido→isocloso structural continuum

Reaction of the arachno-[B9H14]– or nido-[B9H12]– anions with [IrCl(PPh3)3] at ca. 298 K gives, in addition to previously reported species, pale violet [7,7,9-(PPh3)3-isonido-7-IrB9H10]2 in yields of ca. 2%. Single crystal X-ray diffraction analysis and multinuclear NMR spectroscopy reveal a ten-vertex {IrB9} cluster of an ‘isonido’ type that is based upon the closo eleven-vertex structure of [B11H11]2– from which a four-connected vertex is removed to generate a four-membered open face. There are two fluxional bridging hydrogen atoms associated with the open face. Thermolysis at ca. 355 K of solutions in 1,1,2,2-tetrachloroethane of yellow [5,7-(PPh3)2-5-H-5-(o-Ph2P[graphic omitted]]4 result in loss of hydrogen and the formation of deep purple [8-Cl-7,9-(PPh3)2-7-(o-Ph2P[graphic omitted]0]5(0–5%) and royal blue [7,9-(PPh3)2-7-(o-Ph2P[graphic omitted]0]6(0–5%). Single-crystal X-ray diffraction shows that compounds 5 and 6 also have isonido cluster structures, although 5 does not have bridging hydrogen atoms on the open face, suggesting that any extra electrons required for it to be isoelectronic with 2 and 6 may originate from the metal vertex. The structure of the crystal of compound 6 examined was found to contain ca. 25 mole % of the isostructural 3-chloro derivative 6a. The ten-vertex clusters 2, 5 and 6 are part of a structural continuum ranging from closo through isonido to isocloso. It is proposed that these isonido compounds represent intermediates in a variety of reactions involving nido to isocloso cluster oxidations and nido to nido rearrangements.

Nine-vertex polyhedral iridamonocarbaborane chemistry. Products of thermolysis of [(CO)(PPh3)2IrCB7H8] and emerging alternative cluster-geometry patterns

Thermolysis of [7-(CO)-7,7-(PPh3)2-7,1-IrCB7H8]1 at 250 °C resulted in isomerisation to give orange air-stable [7-(CO)-7-H-7,9-(PPh3)2-7,1-IrCB7H7]2 and its 6-(PPh3) isomer 3 as the major products. The compounds were characterised by NMR spectroscopy and single-crystal X-ray diffraction analysis on 1 and 3. The CH2Cl2 disolvate of 1 is monoclinic, space group P21/n, with a= 1394.33(10), b= 1276.81 (13), c= 2393.5(2) pm, β= 94.163(9)°, and Z= 4, and the structure was refined to R(Rg)= 0.0351 (0.0384) for 5991 reflections with I > 2.0σ(I). The CH2Cl2 monosolvate of 3 is triclinic, space group P, with a= 1150.39(11), b= 1177.08(13), c= 1498.3(2) pm, α= 88.192(9), β= 89.506(8), γ= 80.720(9)°, and Z= 2. and the structure was refined to R(Rg)= 0.0299(0.0311) for 5864 reflections with I > 2.0σ(I). The nine-vertex {IrCB7} cluster structures of 1 and 3 have quadrilateral open faces (B–B ca. 220 pm) and therefore ‘isonido’ geometries although of formal closo constitution. The cluster opening is briefly discussed in the context of a nine-vertex closo–isonido–isocloso structural continuum, in the context of other contemporaneously recognised structural continua in twelve-, eleven-, ten-, and eight- vertex boron cluster chemistry, and thence in the context of emerging general structural patterns that interrelate the isocloso, isonido and isoarachno cluster geometries.

The synthesis of bridged-ring carbo- and hetero-cycles via palladium catalysed regiospecific cyclisation reactions ☆

Abstract A catalyst system comprising 10 mol % (Pd(OAc) and 20 mol % PPh3 effects the cyclisation of aryl halides onto proximate alkenes via 5-, 6-, and 7-exo-trig, and 7-endo-trig processes giving a variety of bridged-ring carbo- and hetero-cycles in excellent yield. Double bond isomerisation in the product is rarley encountered and may be suppressed by the addition of Tl(1) salts. One example of diastereospecific bis-cyclisation is given and the crystal structure of 1-aza-2-sulphonyl-3,4-benzobicyc is reported.

X = Y - ZH Systems as potential 1,3-dipoles. Part 37 generation of nitrones from oximes. Tandem intramolecular 1,3-azaprotio cyclotransfer - intramolecular 1,3-dipolar cycloaddition reactions. Class 4 processes.

Abstract Aldoximes and ketoximes containing two alkenyl moieties in different side chains undergo thermal conversion to 5 - and 6 - membered cyclic nitrones, via concerted 1,3 - azaprotio cyclotransfer, followed by stereospecific intramolecular cycloaddition to give tricyclic spiro- and fused- ring systems. An X-ray crystal structure of one such product is reported.

3-Component palladium–indium mediated diastereoselective cascade allylation of imines with allenes and aryl iodidesElectronic supplementary information (ESI) available: experimental details. See http://www.rsc.org/suppdata/cc/b2/b202940e/

A new palladium–indium diastereoselective cascade allylation of imines using allenes and aryl iodides is described; N-tosyl and N-aryl homoallyl amines were obtained in moderate to good yields and excellent diastereoselectivity was observed when enantiomerically pure N-tert-butanesulfinyl imines were employed in the cascade.

Total synthesis of (R,R)-crinan via regiospecific and stereoselective palladium catalysed cyclisation

Abstract The synthesis of (R,R)-crinan from (S)-1-cyclohexenylethan-1-ol is described. The key palladium catalysed step involves a regiospecific 6-exo trig cyclisation which proceeds with 20:1 stereoselectivity for the trans-ring junction over the cis-ring fusion. The ring junction stereochemistry is sensitive to solvent, phosphine and small amounts of water.