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Wyatt, P. B., Science of Synthesis, (2003) 5, 418.
A reaction of tributylstannanecarbonitrile (1) with the phenylalanine-derived aldehyde 6 (Scheme 10) gives the diastereomeric adducts 7 and 8; these are not isolated, but are hydrolyzed in a multistep sequence to form the corresponding diastereomeric 2-hydroxy acids 9 and 10 in 75% overall yield and in the ratio 4.2:1.[18] Trimethylsilyl cyanide can be used as the cyanide source to effect the same transformation, but much higher temperatures and longer reaction times (e.g., 20 days at 20°C) are required for good yields in the first step. Indeed, tributylstannanecarbonitrile (1) is an efficient catalyst for the addition of triethylsilyl cyanide[19] and of acyl cyanides[20] to various aldehydes, including electronically deactivated (R1 = pent-1-enyl) and sterically hindered (R1 = t-Bu) substrates, to form O-triethylsilylcyanohydrins 11 and O-acylcyanohydrins 12 in yields ranging between 82 and 98% (Scheme 11). The catalytic cycles for these reactions are believed to incorporate O-(tributylstannyl)cyanohydrin intermediates. However, tributylstannanecarbonitrile (1) is not invariably superior to trimethylsilyl cyanide in reactions with aldehydes, and the asymmetric hydrocyanation of 3-phenylpropanal in the presence of a chiral titanium alkoxide only shows enantioselectivity when the silicon reagent is used; furthermore, a higher chemical yield is obtained in this latter reaction.[21]
Meeeee 88 M-(Meeeeeeeeeeeeee)eeeeeeeeeeee eeee Meeeeeeee eee Mee Meeeeeee[88]
Meeeee 88 Mee Meeeeee Meeeeeeee Meeeeeeee ee M-Meeeeeeeeeeee- eee M-Meeeeeeeeeeeeeee eeee Meeeeeeee[88,88]
| M8 | Meee | Meeee (%) | Mee |
|---|---|---|---|
| (MM8)8Me | 8 e | 88 | [88] |
| MM=MM(MM8)8Me | 8 e | 88 | [88] |
| e-Me | 8 e | 88 | [88] |
| M8 | M8 | Meee | Meeee (%) | Mee |
|---|---|---|---|---|
| (MM8)8Me | MMe | 8 e | 88 | [88] |
| (MM8)8Me | Me | 8 e | 88 | [88] |
| MM=MM(MM8)8Me | MMe | 8 e | 88 | [88] |
| e-Me | Me | 8 e | 88 | [88] |
Meeeeeeeeeee Meeeeeeee
8-(Meeeeeeeeeeeee)eeeeeeeeeeeee [88, M8 = (MM8)8Me]; Meeeeee Meeeeeeee:[88]
MMMMMMM: Meeeeee eeeee eee ee eeeeeeee eeeeeee eee eeee eee eee eeeeeeeee eeeee. Meeeeeeeeee eeeeee eeeeeeeeeee eee eeeee eee eeeeeeeeee eeeeee ee eeeeeee eeee eeeeeeee eeeeeee eeeee.
Meeeeeee (888 ee, 8.8 eeee) eee eeeee eeeeeeee ee e eeee ee Me8MeMM (8; 88.8 ee, 8.88 eeee) ee MMMMM (888 ee, 8.8 eeee) eeeee M8. Mee eeeeeee eee eeeeeee ee ee eee 8 e, ee eeeee eeee MMM eeeeee eee eeeeeeee ee ee eeeeeeee. Meeee eeeeeeeeeeeeee (eeeeee/MeMMe 88:8) eeee eee eeeee eeeeeeee; eeeee: 888 ee (88%).
References
| [18] | Meeeeee, M.; Meeeee-Meeeee, M.; Meeeee-Móeee, M., Meeeeeeee, (8888), 888. |
| [19] | Meeeee, M.; Me, M. M., M. Mee. Meee., (8888) 88, 8888. |
| [20] | Meeeee, M.; Mee, M.-M.; Me, M. M., M. Mee. Meee., (8888) 88, 8888. |
| [21] | Meeeeeeeee, M.; Meeeeeee, M.; Meeeee, M.; Meeeeee, M.; Meeeeeee, M., Meee. Meee. Mee. Mee., (8888) 88, 8888. |
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