J. I. G. Cadogan

Synthesis of organophosphorus compounds via silyl esters of phosphorous acids

Abstract The addition of trimethylsilyloxy phosphorus (III)derivatives generated in situ to imines at room temperature provides a mild selective and high yielding route to α-aminoalkylphosphorate and α-aminoalkylphenylphosphinate esters. Isocyanates and carbodiimides react similarly to give phosphonoureas and phosphonoguarnidines respectively aldehydes and ketones are much less reactive and cyanides are inert.

Chemical transformations on the surface of [60]fullerene: Synthesis of [60]fullereno[1′,2′:4,5]oxazolidin-2-one

Abstract Base-induced α-elimination from substituted O -4-nitrophenylsulfonylhydroxamic acids has been used as a mild source of nitrenes for capture by [60]fullerene; rearrangment of the resulting [60]fullereno[1′,2′:2,3]aziridine bearing a N -ethoxycarbonyl grouping under the influence of phenol/chlorotrimethylsilane results in the quantitative formation of the title compound which can be cleaved to yield 1-hydroxy-2- N -methylamino[60]fullerene.

Asymmetric Diels-Alder reactions employing modified camphor-derived oxazolidin-2-one chiral auxiliaries

Abstract Transposition of the dormant methyl group from C-1 in chiral oxazolidin-2-one 2 to C-7 in a six step synthetic sequence from (1R)-camphor 5 creates a novel transfigomer 4 with sufficient π-topological bias to induce excellent levels of asymmetric induction in Lewis-acid catalysed Diels-Alder reactions of its α, β-unsaturated carboximide derivatives with cyclopentadiene. Further modification of 4 by replacement of the C-7 methyl group with an ethyl substituent raises the level of diastereoselectivity for the acrylate derivative 11a from 81 to >95% d.e..

Highly regio- and stereo-specific preparation of a new carbohydrate-based 1,3-oxazin-2-one by the INIR method and its applications in some asymmetric transformations

Abstract Preliminary experiments show that a new gulonic acid-derived 1,3-oxazin-2-one, prepared by an intramolecular nitrene insertion reaction (INIR) method, serves to control both asymmetric aldol and Diels-Alder reactions with excellent stereo-selection.

Preparation of enantiomerically pure fructose-derived 1,3-oxazin-2-one by INIR methodology and its application as a chiral auxiliary in some model asymmetric reactions

Abstract A newly developed fructose-based homochiral 1,3-oxazin-2-one reagent prepared via a regioselective and stereoselective intramolecular nitrene insertion reaction (INIR) exerts smooth stereocontrol resulting in high levels of asymmetric induction and chemical yield in various synthetic transformations including aldol, Diels-Alder cycloaddition and α-bromination reactions.

Intramolecular ring cleavage of chiral terpenoid-derived oxazinone via asymmetric anti-aldol reaction: Unexpected entry to a N-substituted tetrahydro-1,3-oxazine-2,4-dione derivative

Abstract In the presence of excess Bu 2 BOTf to promote anti -selectivity, an asymmetric aldol reaction with a homochiral terpenoid-derived 1,3-oxazin-2-one as the chiral control element results unexpectedly in ring cleavage by an intramolecular process to form a N -substituted tetrahydro-1,3-oxazine-2,4-dione in virtually quantitative yield.

Chemical transformations on the [60] fullerene framework via aziridination processes

Abstract Isolation of closed 6,6-bridged aziridinofullerenes 2 by reaction of [60] fullerene with singlet oxycarbonylnitrenes is accompanied by small amounts of previously undetected closed 5,6-adducts 4 , thought to arise by trapping of triplet nitrenes. Isomerization of the 6,6-bridged adducts to the corresponding oxazolo[4′,5′:1,2] [60] fullerene derivatives 3 occurs upon heating with the exception of the tert-butoxycarbonyl adduct which eliminates isobutene and CO 2 to yield the parent aziridinofullerene C 60 NH 6 .

3-Aryl-2,3-dihydro-1,3,2-benzothiazaphosph(V)oles. A new class of phosphoranes

Aryl 2-nitrophenyl sulphides react with tervalent phosphorus reagents to give the novel oxythiaza-phosphoranes (2; X = S) which easily isomerise to the phosphoramidates (3), expect in the case of the more stable bicyclic analogues, e.g., 3-(2,6-dimethylphenyl)-2,2-ethylenedioxy-2-phenyl-2,3-dihydro- 1,3,2-benzothiazaphosp(V)ole(5; Y = H), which by X-ray crystallography, is much disorted towards a square pyramid.

Synthesis of 1,2-azaphosphetidines

Photolytic or rhodium catalysed decomposition of α-diazo-β-ketophosphonamidates and intramolecular C–H insertion of the resulting carbene intermediates is the key step in the synthesis of mono and bicyclic 1,2-azaphosphetidines.

Reduction of nitro- and nitroso-compounds by tervalent phosphorus reagents. Part 16. Formation and reactions of 2,3-dihydro-1,3,2-benzothiazaphosph(V)oles [amino(thiyl)phosphoranes]

In contrast to the corresponding ethers, which give 3-aryl-2,3-dihydro-1,3,2-benzoxazaphosph(V)oles [amino(oxy)phosphoranes](1; X = O) on reaction with phosphorus(III) esters, aryl 2-nitroaryl sulphides give N-aryl-N(2-alkylthiophenyl)phosphoramidates (4). In addition to N–S heterocycles. Yields of (4) are high (70%) when O-blocking methyl groups are present. Using 31P Fourier-transform n.m.r. spectroscopy we have shown that compounds (4) are probably derived via the intermediacy and isomerisation of amino (thiyl)phosphoranes (1; X = S). This has been confirmed, using 2-phenyl-1,3,2-dioxaphospholan, by the isolation of the novel 2,3-dihydro-2-phenyl-3-(2,4,6-trimethylphenyl)-1,3,2-benzothiazaphosph(V)ole-2-spiro-2′-1′,3′,2′-dioxaphospholan (6; Q = Y = Me) and its 2,6-dimethylphenyl- and 2,6-dimethoxyphenyl-analogues (6; Q = Me, Y = H and 6; Q = MeO, Y = H) in 32–76% yield. These do not isomerise to amidates corresponding to (4). The use of methyl diphenylphosphinite (Ph2POMe) in boiling toluene led to the first monocyclic amino (thiyl)phosphoranes, 2,3-dihydro-2,2-diphenyl-3-(2,6-dimethylphenyl)-2-methoxy-1,3,2-benzothiazaphosph(V)ole (7 Ar = 2,6-Me3C6H3; 51%) and its 2,4.6-trimethylphenyl analogue (7; Ar = 2,4,6-Me2C6H2; 48%). In boiling cumene (153 °C) these isomerised into N-(2,6-dimethylphenyl)-N-(2-methylthiophenyl)-PP-diphenylphosphinamidate (8) and its trimethylphenyl analogue. A kinetic study, using a programmed n.m.r. technique, showed that this reaction is first order (105k1 at 451 K = 2.4 ± 1.2 s–1), the high activation energy (Eact. 220 ± 60 kJ mol–1) pointing to a rate-determining fission of the phosphorane ring to give a quasi-phosphonium betaine (10), followed by fast alkyl transfer.By-products in the formation of (7) and (8) from methyl diphenylphosphinite and aryl 2-nitrophenyl ethers include N-(2,6-dimethylphenyl)-N-(2-thiophenyl)-PP-diphenylphosphinamidate (11), formed by acidic hydrolysis of (7); 2-(2,6-dimethylphenylthio)phenylimino-PP-diphenyl-P-methoxyphosphorane (14) and its thermally derived isomer, N-methyl-N-2-(2,6-dimethylphenylthio)phenyl-PP-diphenylphosphinamidate (17), and products of the hydrolysis of (14), N-2-(2,6-dimethylphenylthio)phenyl-PP-diphenylphosphinamidate (13) and the derived amine (12). The formation of 2-methylthio-2′,6′-dimethyldiphenylamine (15) is attributed to methylation of the thioquinone imine (16) postulated as an intermediate in the reaction. Analogous products were obtained from the 2,4,6-trimethylphenyl homologue.The spirophosphoranes (6) exhibit classical temperature-dependent ligand reorganisation observable by n.m.r. with Tc= 110–126°C and ΔG= 80.4–89.8 kJ mol–1. Compounds (7) exhibit solvent chemical-shift changes from –37.8 δ(CDCl3) to +72.4 [(CF3)2CHOH–CDCl3] indicating ring fission to the isomeric quasi-phosphonium betaines.