Enantiomerically Pure Tertiary Alcohols by TADDOL-Assisted Additions to Ketones—or How to Make a Grignard Reagent Enantioselective
✍ Scribed by Dipl. Chem. Beat Weber; Prof. Dr. Dieter Seebach
- Publisher
- John Wiley and Sons
- Year
- 1992
- Tongue
- English
- Weight
- 436 KB
- Volume
- 31
- Category
- Article
- ISSN
- 0044-8249
No coin nor oath required. For personal study only.
✦ Synopsis
Ru(CNtBu)
, (CH,Ph),] (9) and [Ru(CNfBu),(SiMe,Cl),] (10) were both isolated in good yield (78 % and 71 %, respectively). NMR spectra indicate that 10, like 4 and 7, is formed as the trans isomer, while 9, surprisingly, is formed as the cis.
Extensions of these reactions to more complex alkyls have already, for example, led to the preparation of five-membered metallacycles. Stoichiometric quantities of a,w-dihaloalkyls such as 1,4-dibromobutane and a,a'-dichloro-a-xylene were added to freshly prepared solutions of K,-6 to give the respective complexes 11 and 12 in reasonable yield (40 % each).
The accessibility of K,-3 and K,-6 as reactive intermediates supports our previous suggestion that the ability of isocyanides to stabilize metals in negative oxidation states has been severely underestimated. The chemistry of the (isocyanide)metalates appears as rich and diverse as that of carbonylmetalates. The successful preparation of a range of Sn, Si, and C-centered derivatives of K,-3 and K,-6 more specifically supports the analogy between these complexes and tetracarbonylferrate. Thus the path to other (isocyanide)ruthenates with other functional groups has been paved.
Experimental Procedure
4: A solution of 2 (0.35 g, 0.5 mmol) in T H F (25 mL) was reduced by dropwise addition of 4.2 molar equiv of a 0.47 M solution of K[C,,H,] in THF (4.25 mL) at -78°C to give a clear, burgundy-red solution. Dropwise addition of Ph,SnCI (0.39 g, 1 mmol) in THF (10 mL) gave a clear tan solution, which was warmed to room temperature, and the solvent was removed under reduced pressure. The product 4 was extracted into warm hexane. When the solution was slowly cooled to -78 "C. white needles (0.49 g, 0.3 mmol) formed. 7,9, 10, 11, and I2 were prepared by procedures similar to those used to prepare 4.