Matteson Reactions
The Matteson epoxidation allows the preparation of oxiranes from carbonyl compounds and (bromomethyl)lithium.
The Matteson homologation allows the conversion of boronic esters by the insertion of methylene into the C–B bond.
General features: 1. The (bromomethyl)lithium species is generated in situ by the addition of butyllithium to dibromomethane in the presence of a suitable substrate at –78 ºC. 2. (Chloromethyl)lithium, generated by the addition of n-BuLi to DCM, is sometimes employed instead. However, (bromomethyl)lithium offers significant advantages over the previous one in some applications. 3. Aldehydes or ketones yield oxiranes, while boronic esters without functional substituents undergo methylene insertion into the carbon-boron bond. 4. Boronate complexes do not rearrange at −78 °C. This prevents multiple insertions of (dihalomethyl)lithium as any excess reagent decomposes before the homologated boronic ester has been formed. 5. The electrophilic nature of boron results in an efficient ate-complex, inhibiting side reactions such as β-elimination.
Matteson Reactions
Reaction Mechanism
Matteson epoxidation: Addition of n-butyllithium, n-BuLi, to equimolar amounts of dibromomethane generates the lithium carbenoid that inserts into the carbonyl compound. Then, the intermediate alkoxide attacks the electrophilic halomethyl group generating the three-membered cycle.
Matteson homologation: Addition of the bromomethyllithium at the boron center followed by a 1,2-rearrangement of the ate complex.
Experimental Procedure
To a stirring solution of the aldehyde (95.0 mmol, 1.0 eq) in THF (300 mL) was added dibromomethane (1.2 eq) at room temperature. Then the solution was cooled to -78 ºC in a dry ice/acetone and n-butyllithium (2.50 M in hexanes, 1.05 eq) was added slowly over 5 minutes. The reaction was naturally warmed to room temperature over 16 h and quenched with saturated NH4Cl solution. The aqueous layer was extracted with Et2O. The combined organic layers were washed with brine, dried over anhydrous MgSO4, filtered and concentrated by rotary evaporation. The residue was purified by FCC to afford the desired epoxide (65% yield).
More Examples
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