The commercial synthesis of a useful heterocyclic derivative requires treatment of a mixture of aldopentoses (derived from corncobs, straw, etc.) with hot acid under dehydrating conditions. The product, E, has ¹H NMR spectrum E, shows a strong IR band at 1670 cm^-1, and is formed in nearly quantitative yield. Identify compound E and formulate a mechanism for its formation. 

Compound E is a valuable synthetic starting material. The following sequence converts it into furethonium, which is useful in the treatment of glaucoma. What is the structure of furethonium? 

Treatment of a 3-acylindole with LiAlH₄ in (CH₃CH₂)₂O reduces the carbonyl all the way to a CH₂ group. Explain by a plausible mechanism.

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1Η ΝMR 1 H 1 H IH 9.6 9.5 7.6 7.2 7.1 6.5 1H (CH3)4Si 9.5 9.0 8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 300-MHz 'H NMR spectrum ppm (ð) E