Nitrile Oxides, Nitrones, and Nitronates in Organic Synthesis : Novel ...

620 NITRONATES
Table 3.18 Double silylation of AN. Optimal procedures for synthesis of BENAs
Proce- BENA Yield
Entry R 1 R 2 R 3 Si X Conditions dure a 333 %
1 Me H H Me3Si Cl 20 ◦ ,70h A a 77
2 Me H H Me3Si Br 20 ◦ ,40h B a 92
3 H H H Me3Si Br 0 ◦ ,20h B b 97
4 H Me H Me3Si Br −30 ◦ 5 H CH2CO2-
Me
H Me3Si Br
,48h
−30
B c 89
◦ ,92h B d 97
6 (CH2)2- H H Me3Si Br 20
CO2Me
◦ ,20h B e 90
7 Ph H H Me3Si Br 0 ◦ 8 H CHMe- H Me3Si Br
,42h
−30
B f 88
CO2Et
◦ , 120 h B g 79
9 -(CH2)4- H Me3Si Br −30 ◦ 10 CH(Pr
,20h B h 60
i )- H H Me3Si Br 20 ◦ ,17daysc B i 62
OSiMe3
11 CO2Et H H Me3Si OTf −75 ◦ ,5h C j 94
12 H CO2Me H Me3Si OTf −75 ◦ , 2.5 h C k 87
13 CO2Et Me H Me3Si OTf −50 ◦ ,4h C l 92
14 H CO2Me H Me3Si OTf −75 ◦ ,5h C m 87
15 H CO2Me PhCOCH2 Me3Si OTf −75 ◦ , 1.5 h C n 71
16 Me CO2Me H Me3Si OTf −30 ◦ ,3h C o 85
17 H CH2=C-
(OSiMe3) c
H Me3Si OTf −75 ◦ ,2h C p 84
18 H H H Me2Bu t Si OTf 0 ◦ ,4h C b’ 92
19 Me H H Me2Bu t Si OTf 0 ◦ ,3h C a’ 93
20 CO2Et H H Me2ButSi OTf −40 ◦ 21 H CHMe- H Me2Bu
,2h C j’ 55
CO2Et
tSi OTf 0 ◦ ,3h C g’ 93
22 CH(Pri )- H H Me2ButSi OTf 20 ◦ ,6daysb C i’ 78
OSiMe3
23 Me CO2Me H Me2Bu t Si OTf 0 ◦ ,3h C o’ 75
24 Ph H H Me2Bu t Si OTf 0 ◦ ,3h C f’ 85
25 Br H H Me2Bu t Si OTf 0 ◦ ,4h C r’ 72
26 Br H H Me3Si OTf 0 ◦ ,48h C r 85
27 Cl n-C5H11 H Me2Bu t Si OTf 0 ◦ ,4h C s’ 90
28 I n-C5H11 H Me2Bu t Si OTf 0 ◦ ,4h C t’ 75
29 F n-C5H11 H Me2Bu t Si OTf 0 ◦ ,24h C u’ 75
a A–Me3SiCl/Et3N inMeCN;B-Me3SiBr/Et3N in 1,2-dichloroethane; C - SiOTf /Et3N inCH2Cl2.
b For SENA→BENA (for run 10: Me3SiCl/DBU, CH2Cl2, 0→20 ◦ C, 0, 5 h).
c Entry 17, for AN, R 2 =MeCO.
For example, BENA (336) can be detected only by NMR spectra of the reaction
mixture. At higher temperature, this nitroso acetal is transformed in solution
into a mixture of oxime (334a) (the rearrangement product) and enoxime (337)
(the elimination product of trimethylsilanol) (469) (Scheme 3.198).
Double silylation of AN (338) with Me3SiBr/Et3N afforded both the usual
BENA (339b), and the product of its rearrangement, nitroso acetal (340b)
(Scheme 3.199), which was detected in the reaction mixture by NMR data.