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The reaction of 1,2-epoxy-1-(p-nitrophenyl)cyclohexane with boron trifluoride–diethyl ether exhibits a pronounced solvent dependence: in benzene it gives a 9 : 1 ratio of cis-2-fluoro-2-(p-nitrophenyl)cyclohexanol to 1-(p-nitrophenyl)cyclopentanecarbaldehyde, which does not change with reaction time; in dichloromethane the cis-fluorohydrin is again the main primary product, but is rapidly converted into the aldehyde in the reaction medium; and in ether about equimolar amounts of cis- and trans-2-fluoro-2-(p-nitrophenyl)cyclohexanol are formed. The presence of small amounts of water in the dichloromethane solvent causes the formation of a ca. 6 : 4 mixture of cis-fluorohydrin and aldehyde, the composition of which changes little with reaction time. This solvent dependence of the reaction can be useful for preparative purposes. A reaction mechanism is suggested.

The crystal structure of the title compound (4) has been determined by three-dimensional diffraction methods. Crystals are orthorhombic, space group P212121 with Z= 4, unit cell dimensions a= 23.771(7), b= 8.833(2), c= 7.943(7)A. The structure has been solved by direct methods and refined by least-squares to R 0.051. The relevant molecular parameters are compared with those of other Δ3-cephem derivatives. In particular the same distortions of the β-lactam ring are observed; the lactam-nitrogen atom is out of the plane of its bonded carbon atoms by 0.20 A.

The R configuration of the side-chain linked to the C(4) atom of the Δ3–cephen derivative (6) was unequivocally established by means of crystal-structure determination. Crystals are monoclinic, space group P2, with Z= 4, unit-cell dimensions a= 11.293(4), b= 20.211(4), c= 8.927(3)A. In the asymmetric unit of (6) two independent molecules (6a and b) are present. The structure was solved by direct methods and refined by least-squares to R 0.042. The relevant molecular parameters are compared with the corresponding ones of the ketone (1).

The azetidinone disulphide (1b), a structural analogue of Kamiya's disulphide (1a), has been synthesized. Some cyclization reactions of the disulphides (1)(Br2 in CH2Cl2 and AcOAg in ClCH2CO2H–CH2Cl2) leading to penam and cepham derivatives through episulphonium ions (2), have been studied. The data obtained show that changing the substituent X in (1a) and (1b) brings about changes in the distribution of the positive charge in the intermediate episulphonium ions (2a) and (2b), and thus affects to some extent the regioselectivity of the episulphonium ring opening and the chemical behaviour of (1a) and (1b).

Correlation of the logarithms of the ratios of cis to trans diols formed in the acid-catalysed hydrolysis of 13 1-arylcyclohexene oxides with the σ+ constants indicates that there is a higher degree of carbocationic character in the transition state leading to the cis-product.

A series of erythro- and threo-ethyl 3-hydroxy-2-methyl-3-(p-substituted phenyl)butyrates has been prepared The 1H n.m.r. spectra of these compounds and their use in assigning diastereoisomeric configurations are discussed