Page 1014 - Advanced Organic Chemistry Part B - Reactions & Synthesis

990 One example of this type of reaction is the photolytically initiated decomposition of
N-chloroamines in acidic solution, which is known as the Hofmann-Loeffler-Freytag
CHAPTER 10 371
reaction. The initial products are -chloroamines, but these are usually converted
Reactions Involving to pyrrolidines by intramolecular nucleophilic substitution.
Carbocations, Carbenes,
and Radicals as Reactive
Intermediates + +
initiation RCH CH CH CH NHCH hν RCH 2 CH CH CH NHCH + Cl .
2
3
2
2
2
2
2 .
3
2
Cl
+ +
propagation CH CH CH NHCH RCHCH CH CH NH CH
RCH 2 2 2 2 . 3 . 2 2 2 2 3
+ +
RCHCH CH CH NH CH + RCH CH CH CH NHCH
. 2 2 2 2 3 2 2 2 2 3
Cl + +
CH CH NH CH + RCH CH CH CH NHCH
RCHCH 2 2 2 2 3 2 2 2 2 . 3
Cl
base-catalyzed
cyclization + NaOH
2
RCHCH 2 CH CH NH CH 3 R
2
2
N
Cl
CH 3
A closely related procedure results in formation of -lactones. Amides are
converted to N-iodoamides by reaction with iodine and t-butyl hypochlorite. Photolysis
of the N-iodoamides gives lactones via iminolactone intermediates. 372
R R
O hν O H 2 O
RCH (CH ) CNHI RCH(CH ) CNH 2 O O
2 2
2
2 2
+
I I – O
NH 2
Steps similar to the Hofmann-Loeffler reaction are also involved in cyclization of
N-alkylmethanesulfonamides by oxidation with Na S O in the presence of cupric
2 2
4
ion. 373
–e –
RCH (CH ) NHSO CH 3 RCH (CH ) NSO CH 3 RCH(CH ) NSO CH 3
2 3 .
.
2 3
2
2
2
2 3
2
2
–H +
H
Cu 2+
RCH(CH ) NHSO CH 3 RCH(CH ) NHSO CH 3
.
2
2 3
2
2 3
R
+
N
SO CH 3
2
There are also useful intramolecular functionalization methods that involve
hydrogen atom abstraction by oxygen radicals. The conditions that were originally
developed involved thermal or photochemical dissociation of alkoxy derivative of
Pb(IV) generated by exchange with Pb(OAc) . 374 These decompose, giving alkoxy
4
371
M. E. Wolff, Chem. Rev., 63, 55 (1963).
372
D. H. R. Barton, A. L. J. Beckwith, and A. Goosen, J. Chem. Soc., 181 (1965).
373 G. I. Nikishin, E. I. Troyansky, and M. Lazareva, Tetrahedron Lett., 26, 1877 (1985).
374
K. Heusler, Tetrahedron Lett., 3975 (1964).