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Examines the contributions made by Arthur Lapworth to the mechanistic view of organic reactions.

Does Sir Robert Robinson deserve singular recognition as the founder of modern electronic mechanistic thinking in regards to organic reactions?

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The phenomenon of ring-chain tautomerism2 is well known in both natural and synthetic organic compounds, where the ring is five or six membered. Yet it has never been observed experimentally in any system involving a large ring (16 membered or higher), in spite of the fact that such large rings, once formed, are stable. The stability of macrocycles is illustrated by the increasingly large number of naturally occurring many-membered ring compounds being investigated.In particular, the macrolides,3 macrocyclic keto lactones (containing other functional groups as well), bear a structural resemblance to smaller ring tautomers such as phthalaldehydie acid,4 the alkaloid lycorenine,5 and the sugars.As a means of probing for the existence of macrocyclic ring-chain tautomerism, we have synthesized a number of new compounds (1-12), which are described in Table I. These were chosen for study because the corresponding1 ring tautomers would possess the ansa structure, which is known to be stable provided the ring is large.6 It has already been pointed out7a that the keto lactone 13a7b is a good model compound for such ansa ring tautomers derived from 2-10.