Table 1 Optimization of the reaction conditions for Rh-catalyzed asymmetric conjugate additionView full size image

From: Carbon-silicon-switch effect in enantioselective construction of silicon-stereogenic center from silacyclohexadienones

entry

variations from condition Aa

conv. (%)b

4aa/5aab

yield (%)c 4aa

% eed 4aa

1

none

> 99

> 50:1

94

99

2

(R)-segphos

52

> 50:1

46

12

3

(R)-difluorphos

> 99

> 50:1

88

50

4

(R)-binap

> 99

> 50:1

86

40

5

(R)-DM-binap

70

72:28

49

59

6

(R)-DTBM-binap

> 99

59:41

53

99

7

(S,S)-Fc-tfb

< 3

–

0

–

8

without ClSiMe3

< 3

–

0

–

9

at 30 °C

> 99

> 50:1

90

93

  1. aReaction conditions (condition A): 1a (0.20 mmol), PhZnCl (0.60 mmol), ClSiMe3 (0.60 mmol), [RhCl(coe)2]2 (5 mol% Rh), (R)-DTBM-segphos (6 mol%), and THF (2.5 mL) at –10 °C for 12 h.
  2. bThe conversion of 1a and ratio of 4aa/5aa were determined by 1H NMR analysis of the crude reaction mixture.
  3. cIsolated yield.
  4. dThe % ee was determined by HPLC on a chiral stationary phase column. The cis isomer of 4aa has not been detected by 1H NMR of the crude reaction mixture. Considering the accuracy of 1H NMR, the dr (trans:cis) is > 50:1. The absolute configuration of 4aa was determined to be RSi,SC by X-ray crystallographic analysis (CCDC 2344298). coe = cis-cyclooctene. 9-BBN = 9-borabicyclo[3.3.1]nonane. DDQ = 2,3-dichloro-5,6-dicyano-1,4-benzoquinone.