Reverse chemoselective borane reduction of an optically active malonic acid ester

✍ Scribed by Antoine Fadel; Jean-Louis Canet; Jacques Salaun

• Book ID: 104212309
• Publisher: Elsevier Science
• Year: 1989
• Tongue: French
• Weight: 251 KB
• Volume: 30
• Category: Article
• ISSN: 0040-4039
• DOI: 10.1016/s0040-4039(00)70651-4

✦ Synopsis

Reduction of the 2-methyl-2-p-tolylmalonic monoester (+)-2 with the borane-dimethylsulfide complex took place unexpectedly on the ester function,providing the 8-hydroxy-acid (-)-3. This chemoselective reaction proceeded likely through formation of a six-membered ring monoacyloxyborane intermediate 6a and intramolecular hydride transfer. Usually,carboxylic acids are readily reduced by borane 1.2, while carboxylic esters are selectively reduced by lithium borohydride or sodium in ammonia 3.4. A recent report concerning the borane reduction of phenylmalonic acids into 1,3-propanediols 5 prompts us to disclose our unexpected results in this field. Our current investigation concerning the preparation of optically active succinates 6 as efficient precursors of cyclopropane derivatives, which provide valuable building blocks for the total synthesis of natural compounds 7, requires large amounts of p-hydroxy propionic acid derivatives such as 3, for instance. CC'@=3 BH~.MQS CCXXH, COOH KS)-1 (+I-2