Dr L.S. Hart's Research Interests

I am interested in 2 main areas of research: (1) orientational control in aromatic rearrangements; (2) applications of phase-transfer catalysis (ptc).

  1. Compounds of the general formula C6H5-X-Y where e.g. X=O and Y=R, COR, COAr, SO2Ar; or X=NH and Y=R, COR, COAr, SO2Ar, NO, NO2 rearrange under different conditions to give products of the type Y-C6H4-XH, the group Y migrating into the ring, and there has been continuing controversy about the mechanism of these reactions, i.e. about whether the rearrangements are intra- or inter-molecular. The substituent Y usually (though not invariably) migrates to both ortho- and para-positions, if these are free, and in the absence of constraints which may be applied by existing subsituents within the ring. It would be useful to be able to dictate the position in the ring to which Y migrates, which requires a knowledge of the reaction mechanism. This is of practical importance, as the different products of a particular rearrangement often have specific uses, and if the need to separate these products could be avoided, this would be very valuable.

    We have investigated the Fries Rearrangement of phenyl benzoate (X=O, Y=COC6H5, above) most extensively, with briefer examinations of the rearrangement of benzyl phenyl ether (X=O, Y=CH2C6H5, above), and other classes of substrates. In the case of the Fries Rearrangement, we believe we now have a reasonably detailed picture of the mechanisms involved under particular reaction conditions, and are beginning to exploit our understanding by modifying the ortho/para ratio of the products, leading, if possible, to complete orientational control.

  2. Ptc is a simple and widely used chemical technique. We have been using it to synthesise fused-ring heterocyclic cations of the type shown below, and are exploring their chemistry. The possible uses of such compounds are being investigated.

Both (1) and (2) above involve extensive use of analytical techniques, e.g. to provide information about reaction intermediates in (1) and to monitor reactions and separate and identify reaction products in (2). For the mechanistic work, glc has been used extensively for quantitative as well as qualitative analysis, and a wide range of techniques - 1H, 13C, 17O, 27Al nmr, FTIR, and mass spectrometry, as well as isotopic labelling - have been immensely informative. For the ptc and related work, 1H and 13C nmr spectroscopy, including use of more advanced methods, have been particularly valuable. Chromatographic techniques have been widely used, and X-ray diffraction methods have given the final proof of stereochemistry of products separated from mixtures of diastereomers

References:

  1. M.J.S. Dewar and L.S. Hart, Tetrahedron (1970) 26 973, 1001
  2. I.M. Dawson, L.S. Hart and J.S. Littler, J.Chem.Soc. Perkin Trans. II, (1985), 1601
  3. L.S. Hart and C.R. Waddington, J.Chem.Soc. Perkin Trans. II, (1985) 1607
  4. I.M. Dawson, J.L. Gibson, L.S. Hart and C.R. Waddington, J.Chem.Soc. Perkin Trans. II, (1989) 2133
  5. J.L. Gibson and L.S. Hart, J.Chem.Soc. Perkin Trans. II, (1991) 1343
  6. L.S. Hart, C.R.J. Killen and K.D. Saunders, J.Chem.Soc. Chem Comm., (1979) 24
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