SYNTHETIC STUDIES OF LAURENCIN AND RELATED COMPOUNDS. II THE SYNTHESIS OF CIS-2-ETHYL-8-FORMYL-7,8-DIHYDRO-2H-OXOCIN-3(4H)-ONE 3-ETHYLENE ACETAL

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Abstract
The synthesis of the titled hydrooxocinone (2) is described. Hydride reduction of a mixture of methyl 5-ethyl-2,5-dihydro-2-furoates (3) followed by ozonization afforded a dialdehyde mixture, which was submitted to the Robinson-Schöpf condensation to give, after acetylation, three 9-aza-3-oxabicyclo[3. 3 .1]nonanones (5 ∼ 7). cis-Bicyclononanone (5) was further transformed by a modification of the Paquette procedure (5 → 8 → 9 → 10a → 11) to give cis-2-ethyl-8-hydroxymethyl-7, 8-dihydro-2H oxocin-3 (4H)-one (11), which was converted smoothly into the aldehyde (2), one of the most important intermediates for synthesis of laurencin (1).