"Front Matter". In: Organosilanes in Radical Chemistry - Index of
"Front Matter". In: Organosilanes in Radical Chemistry - Index of "Front Matter". In: Organosilanes in Radical Chemistry - Index of
Carbon-Oxygen Double Bonds 105 O OSi(TMS) 3 Ph 1 2 3 OMe (TMS) 3SiH AIBN, ∆ Ph OMe 39 40 Mes Mes Si Si Mes Mes 41 −60 �C Mes Mes Si Ph Mes Si O OMe Mes Scheme 5.7 The use of carbaldehyde 39 as a mechanistic probe The reduction of a-hydroxy ketones 43 to 1,2-diols 44 was achieved in good yield and high diastereoselectivity in favour of the anti product by using Cl3SiH and photolytic conditions [56]. In the proposed mechanism of Scheme 5.8, the addition proceeded via the intermediate adduct 45, which participated in the stereo-controlled hydrogen donation, and via the a-silylether 46, affording 1,2diols in a preferential anti conformation. R OH O Ph Cl 3 SiH hv, 23 �C R Ph O O SiCl2 R OH 43 44 R = cyclohexyl R = 1-naphthyl OH Ph Cl 3 SiH R 45 46 Ph H O O SiCl2 Scheme 5.8 Reduction of a-hydroxy ketones using Cl3SiH 42 OMe Ph OMe acetone, p-TsOH R O O 93%, syn:anti = 63:1 64%, syn:anti = 134:1 A variety of carbonyl compounds react with PhSeSiMe3 in the presence Bu3SnH=AIBN to afford the corresponding hydrosilylation derivatives [59,60]. Generally good yields are obtained only for aromatic substituted aldehydes or ketones. Reactions (5.28) and (5.29) show this case for a few aldehydes
106 Addition to Unsaturated Bonds and a-dicarbonyl compounds, respectively. The proposed reaction mechanism is summarized in Scheme 5.9 and involves the addition of Me3Si: radical to the carbonyl group and subsequent hydrogen abstraction from Bu3SnH. In turn, the Bu3Sn: radical displaced the Me3Si: radical from PhSeSiMe3 and completes the radical reaction cycle (see Section 1.1). X CHO PhSeSiMe 3 Bu 3SnH AIBN, 80 �C X CH 2 OSiMe 3 X = H, Me, OMe, Cl 74 - 85% Ph O O R R = Me R = Ph PhSeSiMe 3 Bu 3SnH AIBN, 80 �C Me 3 Si Me3Si O Bu3SnH O R X R X Me3Si O Me 3Si PhSeSnBu 3 Bu 3Sn PhSeSiMe 3 Ph O O 52% 73% R X R (5.29) (5.30) Scheme 5.9 Propagation steps for hydrosilylation of carbonyl compounds using PhSeSiMe3=Bu3SnH system 5.3.3 RADICAL BROOK REARRANGEMENT The 1,2 migration of the silyl group in Reaction (5.31) somehow recalls the addition of silyl radicals to carbonyl moieties. The initial a-silyl alkoxyl radical 47 could be formally one of the two possible adducts of silyl radical to the carbonyl group, although evidence has never been found for such a reaction. On the other hand, the rearranged carbon-centred radical 48 is identical to the adduct of silyl radical with the carbonyl group. In this section, we briefly describe this rearrangement, which is also called radical Brook rearrangement because it resembles the well known analogous ionic reaction [61].
- Page 59 and 60: Tris(trimethylsilyl)silane 53 Therm
- Page 61 and 62: Tris(trimethylsilyl)silane 55 4.3.1
- Page 63 and 64: Tris(trimethylsilyl)silane 57 A goo
- Page 65 and 66: Tris(trimethylsilyl)silane 59 C(O)C
- Page 67 and 68: Tris(trimethylsilyl)silane 61 radic
- Page 69 and 70: Tris(trimethylsilyl)silane 63 86% y
- Page 71 and 72: Tris(trimethylsilyl)silane 65 RO RO
- Page 73 and 74: Tris(trimethylsilyl)silane 67 O AcO
- Page 75 and 76: Tris(trimethylsilyl)silane 69 Tris(
- Page 77 and 78: Other Silicon Hydrides 71 The reduc
- Page 79 and 80: Other Silicon Hydrides 73 The decre
- Page 81 and 82: Other Silicon Hydrides 75 Ph MeS O
- Page 83 and 84: Other Silicon Hydrides 77 Table 4.6
- Page 85 and 86: Silicon Hydride / Thiol Mixture 79
- Page 87 and 88: Silylated Cyclohexadienes 81 and (4
- Page 89 and 90: References 83 34. Kawashima, E., Uc
- Page 91 and 92: References 85 104. Gimisis, T., Bal
- Page 93 and 94: 88 Addition to Unsaturated Bonds te
- Page 95 and 96: 90 Addition to Unsaturated Bonds ap
- Page 97 and 98: 92 Addition to Unsaturated Bonds 5.
- Page 99 and 100: 94 Addition to Unsaturated Bonds R
- Page 101 and 102: 96 Addition to Unsaturated Bonds Ph
- Page 103 and 104: 98 Addition to Unsaturated Bonds EP
- Page 105 and 106: 100 Addition to Unsaturated Bonds 5
- Page 107 and 108: 102 Addition to Unsaturated Bonds T
- Page 109: 104 Addition to Unsaturated Bonds R
- Page 113 and 114: 108 Addition to Unsaturated Bonds 5
- Page 115 and 116: 110 Addition to Unsaturated Bonds S
- Page 117 and 118: 112 Addition to Unsaturated Bonds T
- Page 119 and 120: 114 Addition to Unsaturated Bonds I
- Page 121 and 122: 116 Addition to Unsaturated Bonds 8
- Page 123 and 124: 118 Addition to Unsaturated Bonds 7
- Page 125 and 126: 120 Unimolecular Reactions 1 Si(H)M
- Page 127 and 128: 122 Unimolecular Reactions t-Bu t-B
- Page 129 and 130: 124 Unimolecular Reactions MeO Si O
- Page 131 and 132: 126 Unimolecular Reactions t-Bu t-B
- Page 133 and 134: 128 Unimolecular Reactions R 1 R 2
- Page 135 and 136: 130 Unimolecular Reactions From the
- Page 137 and 138: 132 Unimolecular Reactions rearrang
- Page 139 and 140: 134 Unimolecular Reactions H 3 C +
- Page 141 and 142: 136 Unimolecular Reactions Br O Si(
- Page 143 and 144: 138 Unimolecular Reactions R3Si C C
- Page 145 and 146: 140 Unimolecular Reactions Me3Si O
- Page 147 and 148: 142 Unimolecular Reactions 43. Albe
- Page 149 and 150: 144 Consecutive Radical Reactions c
- Page 151 and 152: 146 Consecutive Radical Reactions O
- Page 153 and 154: 148 Consecutive Radical Reactions a
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Carbon-Oxygen Double Bonds 105<br />
O<br />
OSi(TMS) 3<br />
Ph<br />
1<br />
2<br />
3<br />
OMe<br />
(TMS) 3SiH AIBN, ∆<br />
Ph<br />
OMe<br />
39 40<br />
Mes Mes<br />
Si Si<br />
Mes Mes<br />
41<br />
−60 �C<br />
Mes Mes<br />
Si Ph<br />
Mes Si<br />
O<br />
OMe<br />
Mes<br />
Scheme 5.7 The use <strong>of</strong> carbaldehyde 39 as a mechanistic probe<br />
The reduction <strong>of</strong> a-hydroxy ketones 43 to 1,2-diols 44 was achieved <strong>in</strong> good<br />
yield and high diastereoselectivity <strong>in</strong> favour <strong>of</strong> the anti product by us<strong>in</strong>g Cl3SiH<br />
and photolytic conditions [56]. <strong>In</strong> the proposed mechanism <strong>of</strong> Scheme 5.8, the<br />
addition proceeded via the <strong>in</strong>termediate adduct 45, which participated <strong>in</strong> the<br />
stereo-controlled hydrogen donation, and via the a-silylether 46, afford<strong>in</strong>g 1,2diols<br />
<strong>in</strong> a preferential anti conformation.<br />
R<br />
OH<br />
O<br />
Ph<br />
Cl 3 SiH<br />
hv, 23 �C<br />
R<br />
Ph<br />
O<br />
O SiCl2 R<br />
OH<br />
43 44<br />
R = cyclohexyl<br />
R = 1-naphthyl<br />
OH<br />
Ph<br />
Cl 3 SiH R<br />
45 46<br />
Ph<br />
H<br />
O<br />
O SiCl2 Scheme 5.8 Reduction <strong>of</strong> a-hydroxy ketones us<strong>in</strong>g Cl3SiH<br />
42<br />
OMe<br />
Ph<br />
OMe<br />
acetone,<br />
p-TsOH<br />
R<br />
O<br />
O<br />
93%, syn:anti = 63:1<br />
64%, syn:anti = 134:1<br />
A variety <strong>of</strong> carbonyl compounds react with PhSeSiMe3 <strong>in</strong> the presence<br />
Bu3SnH=AIBN to afford the correspond<strong>in</strong>g hydrosilylation derivatives<br />
[59,60]. Generally good yields are obta<strong>in</strong>ed only for aromatic substituted aldehydes<br />
or ketones. Reactions (5.28) and (5.29) show this case for a few aldehydes
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