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The possibility of making block copolymers at room temperature from the monomer pairs 2a,b/1, 4/1, 5/1 and 5/3 (1 = norbornene = bicyclo[2.2.1]hept-2-ene; 2a,b = anti- and syn-7-methylbicyclo[2.2.1]hept-2-ene; 4 = methyl endo-bicyclo[2.2.1]hept-5-ene-2-carboxylate; 5 = endo-bicyclo[2.2.1]hept-5-ene-2-carbonitrile; 3 = 1,5-cyclooctadiene) was explored using as initiator of metathesis polymerization in CD2Cl2. The reactions of successive small amounts of the monomers with the catalyst were first followed by 1H NMR to determine the rate of the reaction and the stability of the metal-carbene propagating species. AB and ABA type block copolymers were prepared on this basis and analysed by GPC. An increase in molecular weight after each addition was observed in most cases. Secondary metathesis reactions of double bonds in the polymer chains appear to be significant only for blocks formed from 3.

Polymers of exo,exo-, endo,exo, and endo,endo-5,6-dimethylbicyclo[2.2.1]hept-2-ene monomers were prepared using a selection of eight metathesis catalysts and their structures examined by 13C NMR spectroscopy. Tacticities could be determined for the polymers of the endo, endo and endo,exo monomers and for all three hydrogenated polymers. RuCl3 gave hightrans atactic polymers while ReCl5 gave high-cis syndiotactic polymers, but WCl6/Bu4Sn gave a high-cis atactic polymer of the endo,endo monomer. The endo,exo monomer was unusual in giving polymers of relatively low cis content (fraction of cis double bonds σc ≤ 0,3), and with strong exo,endo (XN) bias except in the case of RuCl3. The parallel with the head, tail (HT) biased polymers of 1-methylbicyclo[2.2.1]hept-2-ene is noted. Polymers of the exo,exo and endo,endo monomers have a blocky cis/trans double bond distribution at moderate cis content. The results are discussed in terms of a mechanism involving propagation by metal-carbene, metal-carbene-olefin and metallacyclobutane complexes.

The resolution of arene oxides, diols and other derivatives of bromohydrins has been markedly improved by the use of bromohydrin esters of (−)-(S)-a-methoxy-a-trifluoromethyl- phenylacetic acid (MTPA).

A 52:48 mixture of syn- and anti-7-ethylbicyclo[2.2.1]hept-2-ene was submitted to polymerization by five metathesis catalysts: RuCl3. 3H20, IrCl3.3H2O, (mes)W(CO)3/EtAlCl2/norbornene epoxide, WCl6/Me4Sn, and ReCl5. Only the anti isomer undergoes ring-opening polymerization, from which it is concluded that propagation occurs by attack on the exo face. The fraction of cis double bonds and tacticities were determined from 13C n.m.r. spectra of the polymers and their hydrogenated products. For the unsaturated polymers these were respectively: 0 00 atactic, 0 21 atactic, 0 43 tactic (c/r, t/m), 059 atactic, 1 00 syndiotactic. The atactic polymers all show a bias towards m dyads for both cis and trans double bonds. This indicates an influence of the configuration of the polymer chain attached to the propagating metal-carbene complex on the stereochemistry of addition of monomer.

The olefinic regions of the 13C NMR spectra of numerous ring-opened polymers of bicyclo[2.2.1]hept-2-ene (norbornene) having cis double bond contents in the range σc = 0,32–0,86, have been analysed in detail. At least six peaks are resolved corresponding to olefinic carbons defined in terms of the double bond sequences tcc, tct + ccc, cct, ttc, ctc + ttt, ctt; for polymers of intermediate cis-content tct and ccc are also resolved. The relative intensities of the cis-centred triads may be accounted for in terms of a single parameter, rc, derived from the observed dyad probabilities. The relative intensities of the trans-centred triads, however, show that at higher cis-contents, the sequence cttc occurs with greater frequency than expected, requiring interpretation in terms of two trans-parameters, rtt and rtc. These results show that the generally noted feature of cis/trans blockiness at moderately high cis-content is sometimes associated with the presence of three kinetically distinct propagating species rather than two. The first is postulated to be the highly cis-directing olefin-metal-carbene complex 4 in which the previously formed cis double bond remains coordinated to the metal centre; this may have both chiral and achiral forms. The second and third are postulated to be isomeric species formed by decoordination of the previously formed trans double bond from the metal centre but in which the initial ligand geometry is governed by the nature of the penultimate double bond: 3tc and 3tt are postulated to have permanent ligands with square pyramidal and octahedral symmetry, respectively. It is shown how the present results and those from related work may be rationalised in terms of this hypothesis.

Eight tungsten-carbene complex catalysts of the type W(CHCMe3)L1L2L3L4, where the ligands L are various combinations of OCH2CMe3, SO3CF3, OSiPh3, Br and I, have been used, in the presence and absence of GaBr3, to polymerize norbornene and six of its methyl derivatives by ring opening. The microstructure of the polymers was determined from their 13C NMR spectra; values of cis content, cis-trans blockiness, ring-dyad tacticity and head-tail bias were derived as appropriate to each system. The results are discussed in terms of electronic and steric effects in the propagating carbene complexes.

The tungsten–carbene complex W(CHCMe3)(OCH2CMe3)2Br2, when mixed with GaBr3, adds various bicyclo[2.2.1]hept-2-enes to form ‘living’ propagating carbene complexes which may be characterized by 1H n.m.r. spectroscopy, and used to make block copolymers.

(–)-trans-4-Bromo-3-hydroxy-1,2,3,4-tetrahydrochrysene has been obtained from the chromatographic separation and cleavage of the corresponding menthyloxyacetyl (MOA) diastereoisomer. The (–)-enantiomer of this bromohydrin has been assigned (3R,4R)absolute stereochemistry and used in the synthesis of (+)-(3S,4R)-chrysene 3,4-oxide. Thermal racemization studies on this arene oxide gave a barrier to racemization (Ea) of 25.15 kcal mol–1 and an activation entropy (ΔS‡) of 0.7 cal mol–1 K–1, in accord with PMO predictions.

(+)-1,2-Epoxy-1,2-dihydrochrysene, a major initial mammalian metabolite of chrysene, has been synthesised and assigned the configuration (1R, 2S). Kinetic studies on the spontaneous thermal racemization of (+)-1,2-epoxy-1,2-dihydrochrysene gave a barrier to racemization (Ea) of 24.8 kcal mol–1. The kinetic results and activation parameters support a thermal racemization mechanism involving an oxepin intermediate.

trans-3,4-Dihydroxy-1,2,3,4-tetrahydrophenanthrene (11) and cis-3,4-dihydroxy-1,2,3,4-tetrahydrophenanthrene (12) have been prepared in optically pure form via: (i) chromatographic separation of the trans-3-bromo-4-menthyloxyacetoxy-1,2,3,4-tetrahydrophenanthrene diastereoisomers (7a), (7b), (ii) conversion of (7a) into the optically pure (+)-tetrahydro-3,4-epoxide (8), (iii)acid-catalysed hydrolysis of (+)-(8) by attack at C-4 to yield (+)-trans-(11) and (–)-cis-(12). Several lines of evidence, including spectral methods and chemical transformation to compounds of known absolute stereochemistry, have been used to assign absolute stereochemistry to all chiral compounds described in the present study. The availability of optically pure diols (11) and (12) has allowed the absolute stereochemistry of the trans- and cis-3,4-dihydrodiol metabolites of phenanthrene (4) and (2) to be determined as (–)-(3R,4R) and (+)-(3S,4R) respectively. Phenantherene 3,4-oxide, an initial mammalian metabolite of phenanthrene prepared from optically pure precursors, was optically active but racemized spontaneously at ambient temperature.

Chrysene 3,4-oxide, a major initial mammalian metabolite of chrysene, now synthesised in optically active form and configurationally assigned, has been found to racemize thermally with an activation energy of 25·2 kcal mol–1, consistent with an earlier perturbational molecular orbital calculation-predicted oxepin intermediate mechanism.

Both the racemic form and the (–)-(3R,4S)-enantiomer of benzo[c] phenanthrene 3,4-oxide have been synthesized in 12 steps from naphthalene. The absolute stereochemistry of the arene oxide enantiomers and related chiral derivatives has been determined by n.m.r. methods. Spontaneous thermal racemization of (–)-benzo[c]phenanthrene 3,4-oxide occurred with a barrier to racemization (ΔG≠29 °C 24.6 kcal mol–1)(1 kcal = 4.184 kJ) in accord with predictions based upon PMO calculations.

ortho-Hydroxylation of chloro- and bromo-benzene occurred in the presence of growing cultures of the fungi Rhizopus arrhizus, Rhizopus stolonifer, and Cunninghamella elegans. The absence of a primary kinetic isotope effect and the presence of the NIH shift are consistent with dihydroarene oxides being initial metabolites. N.m.r. analysis of the deuterium-labelled o-halogenophenol products suggests that enzyme-catalysed epoxidation occurs preferentially at the 2,3-bond.