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36.1.2.2.1.7 Variation 7: Using Meerwein–Ponndorf–Verley-Type Reactions

DOI: 10.1055/sos-SD-036-00032

Cox, L. R.Science of Synthesis, (200836125.

One of the problems with employing ketones in a MeerweinPonndorfVerley reduction is that the alkanol product can be a hydrogen donor for the reverse reaction, which can make it difficult to drive the desired reduction to completion. The lower reactivity of ketones compared with aldehydes also means that larger excesses of reagents and longer reaction times often need to be employed to obtain the secondary alkanols 87 (Table 24).[‌450‌,‌452‌] Many of the additives that improve the efficiency of MeerweinPonndorfVerley reduction reactions with aldehydes are far less successful when ketone substrates are used.[‌450‌] The bis-aluminum reagent 88 (R1=Me), for example, which is an excellent catalyst for the MeerweinPonndorfVerley reduction of aldehydes, gives lower yields of the secondary alkanol ketone reduction product as this acts as a more active hydrogen donor than propan-2-ol. This problem has been circumvented by using 1-phenylethanol as the hydrogen donor and in catalyst preparation (Scheme 72).[‌459‌,‌461‌] Ooi and co-workers introduced aluminum catalyst 89, where this is not a problem and propan-2-ol can now be used as the hydrogen donor without incident.[‌460‌] Simpler aluminum alkoxides, prepared in situ from trimethylaluminum or dimethylaluminum chloride and propan-2-ol in toluene, are also effective in MeerweinPonndorfVerley reductions of ketones (Table 24, entry 5). Interestingly, whilst complexes derived from trimethylaluminum tend to be more active for aldehyde reductions, in the case of ketones, more Lewis acidic systems derived from dimethylaluminum chloride are generally more effective.[‌453‌]

Meeee 88 MeeeeeeeMeeeeeeeMeeeee-Meee Meeeeeeee ee Meeeeee[‌888‌‌888‌,‌888‌,‌888‌,‌888‌,‌888‌]

Meeee M8 M8 Meeeeeee eee Meeeeeeeee Meeee (%) Meeeeeee ­Meeeeeeee eee Meeeeeeeee ee Meeee 88e Mee
8 Me Me Me(MeMe)8 (8 eeeee), MMM (8 eeeee), eeeeeee, ee, 88eee 88 eeeee 8 [‌888‌]
8 Me Me Me(MeMe)8 (8eee%), MMM (8eee%), eMeMM (8 eeeee), eeeeeee, ee, 88e 88 eeeee 8 [‌888‌]
8 Me Me Me(MeMe)8(MMMMM8) (8 eeeee), MM8Me8, ee, 8e 88 eeeee 8 [‌888‌]
8 Me Me Me(MeMe)8(MMMMM8) (8 eeeee), MM8Me8, ee, 88e 88 eeeee 8 [‌888‌]
8 Me Me MeMe8 (88eee%), eMeMM (8 eeeee), eeeeeee, 88°M, 88e 88 eeeee 8 [‌888‌]
8 Me Me eMeMM (8 eeeee), Me(Me)8M8 (8eee%), 888°M, 8e 88 [‌888‌]
8 Me Me eMeMM (8 eeeee), Me(Me)8M8 (8eee%), 888°M, 8e 88 [‌888‌]
8 Me Me Me (8 eeeee), M8 (8eee%), eMeMM, 88°M, 88e 88e eeeee 88 [‌888‌]
8 Me Me Me (8 eeeee), M8 (8eee%), eMeMM, 88°M, 88e 88e eeeee 88 [‌888‌]
88 (MM8)8Me Me Me(MeMe)8 (8eee%), eMeMM, 88°M, 88e 88 [‌888‌]
88 (MM8)8Me Me e-MeMMeM8 (88eee%), eMeMM (8 eeeee), MMM, 88°M, 88e 88 eeeee 88 [‌888‌]

e Meeeeee 88.8.8.8.8.8.

e Me MM.

Meeeee 88 Meeeeeeee MeeeeeeeMeeeeeeeMeeeee Meeeeeeeee ee Meeeeee Meeee Meeeeeeee Meeeee Meeeeeee-Meeeeeee Meeeee[‌888‌‌888‌]

Meeee eeeee eeeeeeeee, ee eeeeeeeeee eeeee eeeeeee eeee eeeeeeeee (Meeee 88, eeeeeee 8, 8)[‌888‌,‌888‌,‌888‌] eee eeeeeee e-eeeee eeeeeeee (eeeeeee 888),[‌888‌,‌888‌,‌888‌,‌888‌] eeee eeee eeee ee eeeeee eeeeeee ee eeeeeeeee eeeeeeee; eeeeee, eeeeeeeee eeeeeeeeeeeeeeee ee eeeee eeeeeeeee, eeeeeeee eeee eee eeee eeeeeeee eeee eeeeeeee eeeeeeeeee, eeeee eeeeeee eeeeeeee eeeeee ee eeeeeee.

Meeeee-8-ee ee 888°M eeeeeee eeeeeeeee ee eee eeeeeee ee eee eeeee eeeeeeee. Meeeeee, eee eeee ee eeeeeeeee ee eeeeeee eeeee eeeee eeeeeeeeee ee eee eeee eee eee eeeeeeee ee eeeeee eeeeeeeeeeeee eeeeee eeeeee ee eeeeeeeee eeeeeee eeeeeee.[‌888‌] Meeeeeee eeeeeee eeee eeee eeeeeeee eeeee eeeeeeeeeeeee eeeeee-8-ee.[‌888‌]

Meeee eeeeeeeeeeeeee eeeeee, eeeeeeeeee eeeee eee eeeeeeee eeeeeeee eeee eeeeeee eeeeeeeeeeee eeeeeeeeee e β-eeeeeeee eeeeeeeeeee, eee eeee eeeeee eeeeeee ee eeeeeeeee eeeeeeee eee e MeeeeeeeMeeeeeeeMeeeee-eeee eeeeeeee eeeeeeeee. Meeeeeeeeeeeeeeeee eeeeeee eee eee eeeee eee eeeeeee eeeeeee 8,8-eeeeeee-8-eeeeeeeeeeeee[8.8.8]eeeeee eee ee eeeeeeeeee eeeeeeee. Meee eee eeeeeee ee eeeeeeeeeeeeeee eeeeeee eee eeeeee ee eeeeeeeeee eeeeeee eeeeee eeeeeeeeeeee (Meeeee 88). Meeeeeeeeeeeeeeeee eeeeeeee eee eeee eeee eeee ee eeeeee eeeeeee ee eee eeeeeeee ee eeee eeeeeeeee.[‌888‌]

Meeeee 88 Meeeeeeeeeeee Meeeee Meeeeeeeeee Meeeeeee ee Meeeeeeeeeeeeeeeee Meeeeeee eee Meeeeee 8,8-Meeeeee-8-eeeeeeeeeeeee[8.8.8]eeeeee ee Meeee Meeeeeee eeee Meeeeeee Meeeeeeee[‌888‌,‌888‌]

Meeeeeeeeeee Meeeeeeee

Meeeeeeeeeeeeeee (88, M8=M8=Me; Meeee 88, Meeee 8); Meeeeee Meeeeeeee:[‌888‌]

Meeeeeeeeeee (8.88e, 88eeee), eMeMM (8.88eM, 88eeee), eee Me(Me)8M8 (88ee, 8.8eeee) eeee eeeeee ee e 88-eM eeeeeeeee eeeee eeeee. Meeee 8e ee 888°M, eee eeeeeeee eee eeeeeeee eee eee eee eeeeeee eee eeeeeeee ee MMMM (eeeeee eee, eeeeee/MeMMe 8:8); eeeee: 8.88e (88%).

8-Meeeeeeeeeeee (88, M8=Me; M8=Me; Meeee 88, Meeee 8); Meeeeee Meeeeeeee:[‌888‌]

Mee eMeMM (8eM) eee eeeee ee e eeeeeee ee Me eeeeee (888ee, 8.8eeee) eee M8 (8888ee, 8.888.88eeee) eeeeeeeee ee e Meeeeee eeee. Me eeeeeeeeee eeeeeeee eee eeeeeeee eeeeee e eee eeeeeee eee eee eeee eeeeee eeee eeeeee-eeeee. Meeee eeeeeeee eee 8e ee ee, e eeee ee eeeeeeeeeeee (888ee, 8.8eeee) ee eMeMM (8eM) eee eeeee. Meeee 88e, 8.8M ee MMe (88eM) eee eeeee. Mee eeeeeee eee eeeeeeeee eeee MeMMe (8 × 88eM), eee eeeeeeee eeeeeee eeeeeeeee eeee eeeeee eeee Me8M8M8 eeee ee eeeeee eeeeeeeee M8, eeee eeee eeeee, eeeee (MeMM8), eee eeeeeeee ee MM; eeeee: 88%.

References


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