Shiv K. Agarwal

General synthetic routes to diarene oxides of polycyclic aromatic hydrocarbons

Abstract Diarene oxides have been synthesised by a single step oxidation of monoarene oxides using dimethyldioxirane, and by a three step cyclization sequence from the appropriate trans -tetrahydrobromoacetate precursors.

Synthesis of arene oxide and trans-dihydrodiol metabolites of quinoline

Racemic samples of 5,6-epoxy-5,6-dihydroquinoline (2)(quinoline 5,6-oxide) and 7,8-epoxy-7,8-dihydroquinoline (4)(quinoline 7,8-oxide) have been synthesised by two methods from the corresponding dihydroquinoline precursors. trans-5,6-Dihydroquinoline-5,6-diol (3) and trans-7,8-dihydroquinoline-7,8-diol (5) were obtained both by multi-step synthetic routes from the corresponding dihydroquinolines and by the direct base-catalysed hydration of the corresponding arene oxides (2) and (4).

The arene oxede-oxepine valence isomerization; a dynamic nmr investigation using a prochiral substituent

Abstract The geminal α-methytene protons in 3-ethylnaphthalene-l,2-oxide show chemical shift nonequivalence in 1 H NMR spectra recorded at ambient temperature consistent with a high barrier to enantiomerization via the orepine tautomer. The methylene protons in α-benzoyloxytoluene-2,3-oxide which are a singlet at ambient temperature split into an AB system at -135 °C and there is evidence of ca . 5% of the oxepine isomer. Lineshape analysis of the coalescing arene oxide AB Signals provides the activation parameters for the valence isomerization/degenerate racemization process: ΔGXXX = 7.6 kcal mol -1 , ΔHXXX = 8.6 kcal mol -l , ΔSXXX= 5.8 cal K -l mol -1 .

Synthesis, spontaneous racemization, and photoisomerization of benzo[e]pyrene 9,10-oxide

Benzo[e]pyrene 9,10-oxide (4) and the isomeric pyreno[4,5-b]oxepine (9) have been simultaneously synthesized from racemic and optically active bromo acetate precursors of known absolute configurations. Spontaneous thermal racemization of benzo[e]pyrene 9,10-oxide (4)[via the undetected oxepine intermediate (15)], and readily occurring photoisomerization of this arene oxide [via the putative arene oxide intermediate (16) to yield pyreno[4,5-b]oxepine (9)] occur as predicted from PMO calculations of resonance energy changes associated with these pericyclic reactions. Optically pure samples of the mammalian metabolites 9,10-epoxy-(12) and trans-9,10-dihydroxy-9,10,11,12-tetrahydrobenzo[e]pyrene (13) have been obtained.

Synthesis of diarene oxides of benz[a]anthracene, chrysene and benzo[c]phenanthrene

A three-step synthetic route to the diarene oxides 5,6;10,11-diepoxy-5,6,10,11-tetrahydrobenz[a]anthracene 18, 5,6;8,9-diepoxy-5,6,8,9-tetrahydrobenz[a]anthracene 22, 3,4;5,6-diepoxy-3,4,5,6-tetrahydrochrysene 26 and 3,4;7,8-diepoxy-3,4,7,8-tetrahydrobenzo[c]-phenanthrene 30, from the corresponding trans-bromo acetate precursors 15, 19, 23, and 27 has been developed. Acid-catalysed isomerization studies to isomeric mixtures of phenols have been carried out.

Preparation of oxepines during direct chemical synthesis and facile oxygen walk reactions of arene oxides: theoretical predictions and experimental evidence

The synthesis of arene oxides and oxepines, and the unexpectedly facile rearrangement of a range of non-K- and bay-region arene oxides of polycyclic aromatic hydrocarbons to isolable isomeric oxepines via a photochemical oxygen walk pathway is reported; oxepine formation can be predicted from PMO calculations which indicate the associated loss of resonance energy during the oxygen walk process.

Conformation and stereodynamics of the oxepine ring system

Low temperature n.m.r. studies on 2-cyano- and 2-ethoxycarbonyl-7-ethyloxepine establish a non-planar ring geometry with a ring inversion barrier of 6.5 kcal mol–1(27.2 kJ mol–1), and provide evidence of a rotational isomerism involving the 2-ethoxycarbonyl substituent; an X-ray crystallographic analysis of 2-t-butoxycarbonyloxepine confirms the non-planar boat geometry.

Synthesis of benzo[g]chrysene, benzo[g]chrysene 9,10-oxide and benzo[g]chrysene 1,2 : 9,10-dioxide

Benzo[g]chrysene has been synthesised and used in the preparation of the K-region arene oxide, benzo[g]chrysene 9,10-oxide. Attempts to synthesise the fjord region arene oxide, benzo[g]chrysene 1,2-oxide, were unsuccessful but a fjord region diarene oxide, benzo[g]chrysene 1,2 : 9,10-dioxide has been obtained.

Synthesis and spontaneous racemization of benz[a]anthracene 3,4-oxide: photochemical oxygen-walk rearrangements of arene oxides of benz[a]anthracene and triphenylene to yield oxepines

Benz[a]anthracene 3,4-oxide 2, when synthesised from optically pure dibromo ester precursors, was found to have racemized spontaneously and was accompanied by anthra[2,1-b]oxepine 14. Photoisomerization of benz[a]anthracene 3,4-oxide 2, triphenylene 1,2-oxide 4 and benz[a]anthracene 1,2-oxide 5 proceeds via an oxygen-walk mechanism to yield anthra[2,1-b]oxepine 14, phenanthro[10,9-b]oxepine 16 and anthra[2,1-f]oxepine 17 respectively.