Al-Isopropoxydiisobutylalane. A Stereoselective Reducing Agent for Reduction of Cyclic Ketones to Thermodynamically More Stable Alcohols

Abstract

In recent years, new developments in the area of stereoselective reduction of cyclic ketones have been exceptionally encouraging. Especially, the reagents developed for conversion of cyclic ketones to the thermodynamically less stable alcohols are extraordinary. 1 However, although several useful reagents have been devised for converting cyclic ketones to the thermodynamically more stable alcohols, 2 generally acceptable synthetic methods for this conversion have still been lacking. In the course of a systematic study of the reducing characteristics of Al-alkoxydiisobutylalane, we have found that Al-isopropoxydiisobutylalane, one of these derivatives, reveals an excellent stereoselectivity in such cyclic ketone reductions to provide the corresponding thermodynamically more stable alcohols. This paper describes this stereoselective reduction.

Meerwein-Ponndorf-Verley Reduction over Heterogeneous Catalysts

“…Cha and Kwon [16] introduced aluminium 2-propoxydiisobutylalane as a selective reducing agent. The thermodynamically more stable isomer is the one with both substituents in the equatorial position rather than one equatorial and one axial.…”

Recent Developments In Meerwein−Ponndorf−Verley and Related Reactions for the Reduction of Organic Functional Groups Using Aluminum, Boron, and Other Metal Reagents: A Review

“…Recently, there have appeared a series of diisobutylaluminum derivatives, such as diisobutylhaloalanes ( 6 ), diisobutylalkoxyalanes ( 7 ), and diisobutylaminoalanes ( 8 ), which were prepared by simple reaction of diisobutylaluminum hydride ( DIBAL-H ) with the corresponding hydrogen halides, alcohols, and amines, respectively (eqs 7−9) These diisobutylaluminum derivatives have achieved a very high chemo-, regio-, and stereoselectivity in the reduction of aldehydes and ketones.…”

Selective Reduction of Cyclohexanones with NaBH4 in β-Cyclodextrin, PEG-400, and Micelles

“…Theoretical studies by Houk and coworkers also support this "flattening rule" [8]. Stereoselective reduction is an ever expanding field especially related to the conversion of cyclic ketones to less thermodynamically stable alcohols [9,10], a niche for synthetic methodology that is still lacking acceptable methods [11]. So far, the asymmetric reduction of prochiral ketones has been successfully achieved by using chirally modified metal hydrides [12].…”