Level 3 – Case 39
262
CO 2 Me
O
HN
R
7
R = MeO, Cl, COMe, F, NO 2 , CF 3
Figure 39.1
2.2 The rates of cyclization of N-(phenylthio)amides N N
8 in the presence of excess
n-Bu 3 SnH were determined (Scheme 39.4). In this radical process, the cyclization product 9 and variable amounts of the reduction compound 10 were
obtained. From the ratios 9:10 (and assuming that the rate of trapping of tin
hydride is the same for all the radicals 11 regardless of R), the relative rate
constants for cyclization of amide radicals 11 were inferred. The values of the
relative rates of cyclization were determined to be 0.66 for R = H, 0.30 for R
= MeO and 0.40 for R = F, respectively. The cyclization proceeded sluggishly with R = COMe and did not proceeded with R = CF 3 .
R
PhSN
O
n-Bu 3 SnH
AIBN
R
N
O
N
O
R
H
H
HN
O
R
8
R = H, MeO, F, COMe, CF 3
9
1 0
11
Scheme 39.4
3 3. 3. C Cy Cy Cy yc y yc yc yc yc yc y y l li li li li l lic ic ic ic i i V Vo Vo V Vo Vo Vo V Vol lt ta ta t ta ta ta ta t tam mm me et tr t tr tr tr tr t t y
ry ry y M Me Me M Me M Me Me M Mea as su ur re re r re re re re r rem me en nt ts ts t ts ts ts ts t t
The oxidation potentials of a series of substituted anilides 8 were determined by
cyclic voltammetry for CH 2 Cl 2 solutions. The observed values were 1.20 V (R =
H), 0.82 V (R = MeO), 1.23 V (R = F), 1.48 (R = COMe) and > 1.57 V (R = CF 3 ).