Asymmetric Induction in Acyclic Systems

Here as well as in the following examples only one enantiomer is shown arbitrarily, although a racemate was used. 

In the first reported example of asymmetric induction using organotitanium reagents, methyltitanium triisopropoxide 6 was reacted with 124 (0 °C/2 h, THF) 72). The ratio of Cram to anti-Cram product 125 126 turned out to be 88 12 (Table 6) which is higher than that observed for CH3MgX (66 34 = or CH3Li (65 35) 9S). 

Variations due to temperature or solvent effects are small. The tri-phenoxy derivative 127 (Table 6) displays the highest degree of selectivity. The zirconium reagents 61 

As already shown in Section B.I, certain organotitanium reagents readily form isolable, octahedral 1 2 adducts with such donor molecules as THF, glyme, thio-ethers, amines and diamines1,19) (Equation 47). In case of methyltitanium trichloride 17, structural data show the methyl group to occupy the equatorial position 96). In order to test whether such molecules undergo stereoselective addition to aldehydes (Equation 47), we reacted 134, 135 and 136 (prepared from TMEDA, glyme and THF, respectively) with 2-phenylpropanal 12491. The 125 126 ratios of 80 20, 82 18 und 85 15 show that the Cram product is preferred in all cases 

Initial studies using 2-methylbutanal 137 show little improvement in going from Grignard to titanium reagents 77). However, the nature of the ligand at titanium has not been varied systematically (Equation 48). 

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For any type of asymmetric inductions in acyclic systems to be successful, the following conditions need to be met ... 

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