Torsional strain involving partial bonds. The stereochemistry of the lithium aluminium hydride reduction of some simple open-chain ketones
✍ Scribed by Marc Chérest; Hugh Felkin; Nicole Prudent
- Publisher
- Elsevier Science
- Year
- 1968
- Tongue
- French
- Weight
- 381 KB
- Volume
- 9
- Category
- Article
- ISSN
- 0040-4039
No coin nor oath required. For personal study only.
✦ Synopsis
The reactions of hydrides and Grignard reagents with simple open-chain alaehydes aa ketones I (L, M, S, and R being groups containing carbon and hy- drogen only) are known to lead predominantly to the diastereoisomers IIA, as predicted by "Cram's rule" (1).
I
IIA IIB
According to current theory, reactions of this type occur via "reactant-like" transition states, in which the nucleophilic part of the reagent (RI-) (2) lies in the n-axis of the carbonyl carbon. Cram (1, 3) assumes that t!to preferred conformations of the transition states ars such that, for stsric rcasons, RI -is remote from the two bulkiest groups L and M, as in CA* and CR', and that CA* ["open-chain model" (1, 3)] is preferred over CB* because it only involves steric strain (a) betweerl L and R, rather than between L and t!fle allegedly bulkier metal-complexed a?ld solvatea carbonyl oxygen (2). Karabatsos (4) has recently criticised this interpretation, and has sugit@ 0 It-___:: 0 H C, 49 H *AH, CA' (cp -O") CB' (cp -0") KA' (cp -300) a* (cp -300