Synthesis of 2,3,4,6,7,8-Hexahydro-5H-1-benzopyran-5-ones and 3-(6-Oxo-1-cyclohexenyl)alkanoic Acids by Reduction of 4,6,7,8-Tetrahydro-2H-1-benzopyran-2,5(3H)-diones

✍ Scribed by Hermann Hombrecher; Paul Margaretha; Paul Tissot

• Publisher: John Wiley and Sons
• Year: 1986
• Tongue: German
• Weight: 218 KB
• Volume: 69
• Category: Article
• ISSN: 0018-019X
• DOI: 10.1002/hlca.19860690723

✦ Synopsis

I211 Genbve 4 (5. V .86) ~ Comparative results on the reduction of 4,6,7,8-tetrahydro-7,7-dimethyl-2H-1 -benzopyran-2,5(3H)-diones 1 are reported. Hydride reduction (LiAIH, in EtzO or NaBH, in i-PrOH) affords 2,3,4,6,7,8-hexahydro-5H-l-benzopyran-5-ones 5 in 30-60 % isolated yield. Photochemical reduction of 1 b and Id (direct irradiation at I = 300 or 254 nm in i-PrOH, or sensitized irradiation in acetone/i-PrOH or benzene/i-PrOH) gives 3-(6-oxo-l-cyclohexen-y1)alkanoic acids 6 in 50-80 %, while Ic affords the isomeric 3-(4,4-dimethyl-6-oxo-l-cyclohexenyl)-4-methyl-4pentenoic acid (9) in 73% isolated yield. Electrochemical reduction (Hg, CH,CN, Bu,N+CIO;, -2.6 V us.

Ag/Ag+) requires more than 4 Farad/mol for the consumption of 1 without any major product being detected.