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DOI: 10.1055/sos-SD-002-00315

Poli, R.; Smith, K. M.Science of Synthesis, (20032312.

In this reaction an al­kyl group R3 is transferred from a suitable metalal­kyl complex to the electrophilic carbon of a car­bon­yl substrate 73 (Scheme 31), resulting in the de­oxy­genation and dimerization to product 74 in a single step.[‌135‌] The substrate 73 can be an aromatic al­de­hyde or ke­to­ne, a conjugated enone, or a ben­zo­ic acid derivative. The al­kyl transfer reagents [R3M] are tungsten(V) compounds formulated as di­al­kyldiprop­oxo(µ-prop­oxo­)tungsten(V) dimers 75. They are obtained in situ by al­kyl­ation of the corresponding di­chlo­ro dimers with lithium or Grignard reagents and they are not isolated in view of their extreme thermolability. A large variety of al­kyl groups, (tri­meth­yl­si­lyl)­meth­yl, and phen­yl have been used as R3, including ones where the β-hydrogen elimination process is possible.[‌60‌] The procedure consists of the addition of the car­bon­yl substrate to 75 in tet­ra­hy­dro­fu­ran at 78°C, followed by warming to reflux and room-temperature base hy­dro­lysis. Various substituents (e.g., meth­oxy, di­meth­yl­amino, fluo­ro, chlo­ro, and hy­dro­xy) on phen­yl groups are tolerated (e.g., see synthesis of 76), but the ni­tro and eth­oxy­car­bon­yl groups are not.[‌135‌] For R3=Me, the car­bon­yl group must be conjugated with an un­saturated group, otherwise the mono­meric car­bi­nol is obtained. With R3=Ph, however, even saturated ke­to­nes yield the additivereductive car­bon­yl dimerization product. Rearrangement products can also be obtained, depending on the substituents linked to the car­bon­yl group; see, for example, the reaction of 2-furaldehyde (77).[‌60‌]

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