Fbc Limited

Michael D Pollard

Stephen R Smythe

Martyn W Whitmore

There is described a process for the production of a compound of formula I, ##STR1## in which at least one each of R.sub.1, R.sub.2 and R.sub.3, and of R.sub.4, R.sub.5 and R.sub.6, represents an electron withdrawing group, or one of R.sub.1, R.sub.2 and R.sub.3 together with one of R.sub.4, R.sub.5 and R.sub.6 form a --CO-- group, and the remainder of R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5 and R.sub.6, which may be the same or different, each represent an electron withdrawing group, alkyl, cycloalkyl, phenyl or phenylalkyl,

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Cambridge, United Kingdom

Michael D Pollard