Studies related to cyclopentanoid natural products. Part 1. Preparation of (4RS)- and (4R)-4-hydroxy-2-hydroxymethylcyclopent-2-en-1-one; a versatile synthetic intermediate
The racemate of 2,5-dihydro-3-hydroxymethyl-2,5-dimethoxy-2-methylfuran (11), prepared from the reaction of 3-hydroxymethyl-2-methylfuran (12b), with bromine in methanol, is converted into the racemate of 4-hydroxy-2-hydroxymethylcyclopent-2-en-1-one (9a) when heated in aqueous dioxan buffered at pH 6.3. Methyl quinate (17b), obtained by treating D-(–)-quinic acid (17a) with methanolic hydrogen chloride, reacts with ammonia in methanol to give quinamide (17c) which affords 1,1′-ON-isopropylidene-3,4-O-isopropylidene-quinamide (27a) in the presence of acetone containing hydrogen chloride. Benzoyl chloride in pyridine transforms compound (27a) into the 5-O-benzoate (27b) which undergoes selective hydrolysis in hot aqueous acetic acid to give 5-O-benzoyl-1,1′-ON-isopropylidenequinamide (26). Sequential treatment of compound (26) with sodium periodate in aqueous tetrahydrofuran (THF) and pyrrolidinium acetate in hot benzene affords (5R,8R)-8-benzoyl-oxy-2,2-dimethyl-4-oxo-1-oxa-3-azaspiro[4.4] non-6-ene-6-carbaldehyde (32). The aldehyde (32) is transformed into (5R,8R)-8-hydroxy-6-hydroxymethyl-2,2-dimethyl-1-oxa-3-azaspiro [4.4]non-6-en-4-one (34a) by reaction with sodium borohydride in THF followed by methanolic sodium methoxide. Hydrazinolysis of the oxazolidinone ring of the last-described compound is effected in boiling hydrazine hydrate to yield (1R,4R)-1,4-dihydroxy-2-hydroxymethylcyclopent-2-ene-1-carbohyd razide (35a). Treatment of the acid hydrazide (35a) with nitrous acid and thermolysis of the derived acid azide (35b) gives (4R)-4-hydroxy-2-hydroxymethylcyclopent-2-en-1-one (9a).