Selective Reduction of Organic Compounds with Al-Trifluoromethanesulfonyldiisobutylalane. Comparison of Its Reactivity with Al-Methanesulfonyldiisobutylalane

Abstract

The new MPV type reagent, Al-trifluoromethanesulfonyldiisobutylalane (DIBAO3SCF3), has been prepared and its reducing characteristics in the reduction of selected organic compounds containing representative functional groups have been examined, and compared its reactivity with that of Al-methanesulfonyldiisobutylalane (DIBAO3SCH3) in order to understand the fluorine-substituent effect on its reactivity. In general, the reactivity of DIBAO3SCF3 appears to be much higher than that of DIBAO3SCH3, apparently due to the acidity increase by the electron-withdrawing fluorine-substituent. The reagent reduced aldehydes and ketones readily, but showed a perfect selectivity in the reduction of α,β-unsaturated aldehydes and ketones to produce the corresponding allylic alcohols in an absolutely 100% purity. In addition, the reagent achieved the regioselective cleavage of phenyl-or/and alkyl-substituted epoxides to the less substituted alcohols in a perfect regioselectivity. Moreover, the reagent also showed an high stereoselectivity in the reduction of substituted cycloalkanones to produce the thermodynamically more stable alcohol epimers exclusively.

Regiospecific Ring-Opening of Unsymmetrical Epoxides to the Corresponding Less Substituted Alcohols by Newly-Devised Meerwein-Ponndorf-Verley Type Reagents

“…Recently, there have appeared a series of diisobutylaluminum derivatives, such as diisobutylhaloalanes (1), [7][8][9][10][11] diisobutylalkoxyalanes (2), [11][12][13][14] diisobutylaminoalanes (3), [15][16][17] diisobutylacetoxyalanes (4 and 5), [49] and diisobutylmethanesulfonylalanes (6 and 7), [18][19][20][21][22] which were prepared by simple reaction of diisobutylaluminum hydride (DIBAH) with the corresponding hydrogen halides , alcohols, amines, acetic acids, and methanesulfonic acids, respectively (Eq. 1-7).…”

“…For example, DIBAOSO 2 CF 3 (7) can reduce a variety of aliphatic and aromatic epoxides readily at 25 o C to the ring-opened alcohol products. [47,48] In this reaction, the less substituted alcohols are produced as a sole product.…”

The Stereoselective Reductions of Ketones to the Most Thermodynamically Stable Alcohols Using Lithium and Hydrated Salts of Common Transition Metals

“…In general, for six-membered rings, bulky reducing agents favor the approach to the carbonyl group via an equatorial trajectory, giving the thermodynamically less stable axial alcohol . Several valuable protocols have been devised for the synthesis of the more stable equatorial alcohols; however, a simple, consistently high-yielding method is unavailable.…”