Science of Synthesis

Harcken, C., Science of Synthesis, (2007) 25, 75.

Diborane reduces carboxylic acids efficiently to alcohols. Certain bulky α,β-unsaturated acids such as tiglic acid [(E)-2-methylbut-2-enoic acid] can be reduced to the aldehyde in useful yields (81%) directly with diborane.[‌63‌] On the other hand, thexylborane [(1,1,2-trimethylpropyl)borane] and derivatives can also reduce carboxylic acids to aldehydes. Thexylborane itself can achieve this transformation, but the reaction is very slow, causing increased side reactions.[‌64‌] Chloro(thexyl)borane and bromo(thexyl)borane reduce carboxylic acids efficiently to aldehydes ‌31‌ (‌Table 3‌).[‌65‌–‌67‌] Reducible functional groups such as halogens (entry 4), nitro (entry 5), and cyano (entry 6) can be retained. Alkenic double bonds undergo partial hydroboration with chloro(thexyl)borane. The reagents are prepared in situ from 2,3-dimethylbut-2-ene and chloroborane–dimethyl sulfide complex or bromoborane–dimethyl sulfide complex, respectively.

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References

Meeeeee Meeeeeeeeee

• 8.Meeeee-Meee, (8888) 8/8e, 888.
• 8.Meeeee-Meee, (8888) M 8, 888.