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

292 NITRONES: NOVEL STRATEGIES IN SYNTHESIS
R 1
SH
+
R 2
N O− +
CH3Cl
20°C
R 1
S
R 2
a: R 1 = H, R 2 = Ph; b: R 1 = H, R 2 = c-C 3H 5;
c: R 1 = H, R 2 = n-C 5H 11; d: R 1 = Ph, R 2 = c-C 3H 5;
e: R 1 = Ph, R 2 = n-C5H11
O
(RO) 2P O
N
R2 R3 +
429
+
N
O − CH 3Cl
65°C, 5h
R 1
S
R 2
427 a–e 428 a–e
Scheme 2.199
R1 − O
−
1. LiP(OR) 2
2. [O]
O
N
R2 R3 +
1. LiP(OR) 2
R = Me, Et; R 1 = Alk, Ar; R 2 = H, Alk, Ar; R 3 = Alk, Ar; R 2 + R 3 = -(CH2)n- (n = 3,4)
O
+
N
H Me
R 1
−
Et 3O + BF 4 −
Scheme 2.200
OEt
N BF4
H Me
−
+
R 1
O
H P
R 2
O
2. [O]
OC 4H 9
R 1 = Ph, n-ClC6H4; R 2 = Me, Ph
Scheme 2.201
O
O
N
(RO) 2P O
N
R2 R3 R1 Me
R 1
N
430
OEt
O
P OC4H 9
A convenient route to β-phosphorus nitroxides involves the 1,3-addition of
trimethylsilyl phosphites (e.g., diethyl) or trimethylsilyl phosphines (e.g.,
diphenyl) to aldo nitrones (e.g., α-PBN, DMPO), or keto nitrones (e.g., 2-Et-
DMPO or 2-Ph-DMPO), to form α-phosphityl- or α-phosphinyl-O-silylhydroxylamines.
Acidic hydrolysis provides the corresponding hydroxylamines which are
easily oxidized to β-phosphorus-nitroxides (690).
Nucleophilic addition of methyl- or phenylphosphite n-butyl- esters to oxoimine
salts, generated by nitrone alkylation of triethyloxoniumtetraßuoro borate
(Meerwein salt), leads to α-aminophosphinic acid esters (Scheme 2.201) (691).
Addition of diethyl phosphites to aldo nitrones derived from chiral α-alkoxy
(Scheme 2.202) and N -Boc-α-amino (Scheme 2.203) aldehydes can be achieved
R 2