Selektive Herstellung von l- oder u-Aldolen aus Äthyl-trityl-keton und aromatischen Aldehyden über Lithium- bzw. Aluminium-Enolate
✍ Scribed by Mümtaz Ertaş; Dieter Seebach
- Publisher
- John Wiley and Sons
- Year
- 1985
- Tongue
- German
- Weight
- 530 KB
- Volume
- 68
- Category
- Article
- ISSN
- 0018-019X
No coin nor oath required. For personal study only.
✦ Synopsis
Selective Preparation of l‐ or u‐Aldols from Ethyl Trityl Ketone and Aromatic Aldehydes through Lithium and Aluminium Enolates, Respectively
The ethyl trityl ketone (1) is deprotonated to the (Z)‐enolate 2 which adds to aromatic aldehydes with relative topicity ul to give the aldols 3(−78°, THF, kinetic control). If, on the other hand, 1 is heated with trimethylaluminium in toluene, the aluminium enolate formed combines with aromatic aldehydes and with cinnamic aldehyde with opposite relative topicity (lk) to the aldols 5 (+20°, toluene, 2 d, precipitation of the aluminium aldolate 4, thermodynamic control). The mechanism is discussed (cf. Fig. 1). The adducts to benzaldehyde (3a, 5a), furfural (3f, 5f), and cinnamaldehyde (3i, 5i) are O‐(2‐methoxyethoxy)methyl (MEM) protected and cleaved by lithium triethylborohydride to the 1,3‐diol derivatives 9–11 with a free primary and a protected secondary OH‐group. Analogous conversions of 1 and other ketones may also be diastereoselective, but turned out to be of less preparative value (see 6–8, 12).