Ritchie' s valuable contributions to heterocyclic chemistry in respect both of his structural studies of naturally occurring substances and of his synthetic work in the field of nitrogen heterocycles have stimulated much work abroad, for example in relation to the synthesis of furoquinoline alkaloids. In the course of his investigations of natural products he has discovered many new alkaloids and coumarins including such quite novel types as the himbaoine group of alkaloids and the dibenzopyrrocolines the occurrence of which had been predicted twenty years previously. Extensive synthetic work on heterocyclic nitrogen compounds includes studies in the phenanthridine series and the synthesis of a number of alkaloids, of particular significance being his extension of the Robinson-Schoff scheme of syntheses under "physiological conditions".