Page 1015 - Advanced Organic Chemistry Part B - Reactions & Synthesis

radicals with reduction to Pb(III). The subsequent oxidation of the radical to a carbo- 991
cation is effected by Pb(IV) or Pb(III).
SECTION 10.3
Pb(OAc) 4 Reactions Involving Free
RCH (CH ) OH RCH (CH ) O Pb(OAc) 3 RCH (CH ) O . + Pb(OAc) 3 Radical Intermediates
2
2 3
2 3
2
2
2 3
–e –
) OH
RCH (CH ) O . RCH(CH ) OH RCH(CH 2 3 R O
.
2 3
2
2 3
+
Current procedures include iodine and are believed to involve a hypoiodite interme-
diate. 375
O O
CH 3 H O Pb(OAc) 4 H O
CH(CH ) I , hν CH(CH )
3 2
3 2
2
O
CH 3 CH CH CH
3 3 3 89%
OH
Ref. 376
The reactions can also be effected by phenyliodonium diacetate. 377 A mechanistic
prototype can be found in the conversion of pentanol to 2-methyltetrahydrofuran. The
secondary radical is most likely captured by iodine or oxidized to the carbocation prior
to cyclization. 378
CH (CH )CH OH CH (CH )CH O. CH CH(CH ) CH OH
2 2
3 .
3
2
2
2
2
2
3
CH 3 O
89%
Alkoxy radicals are also the active hydrogen-abstracting species in a procedure
that involves photolysis of nitrite esters. This reaction was originally developed as a
method for functionalization of methyl groups in steroids. 379
H C H C H
CH 3 C 8 17 O N CH 3 8 17 CH 3 8 17
CH 3 hν CH 2 Δ HON CH
H H H
AcO AcO AcO
H H H
ON O OH OH
It has found other synthetic applications.

375 K. Heusler, P. Wieland, and C. Meystre, Org. Synth., V, 692 (1973); K. Heusler and J. Kalvoda, Angew.
Chem. Int. Ed. Engl., 3, 525 (1964).
376 S. D. Burke, L. A. Silks, III, and S. M. S. Strickland, Tetrahedron Lett., 29, 2761 (1988).
377
J. I. Concepcion, C. G. Francisco, R. Hernandez, J. A. Salazar, and E. Suarez, Tetrahedron Lett., 25,
1953 (1984).
378 J. L. Courtneidge, J. Lusztyk, and D. Page, Tetrahedron Lett., 35, 1003 (1994).
379
D. H. R. Barton, J. M. Beaton, L. E. Geller, and M. M. Pechet, J. Am. Chem. Soc., 83, 4076 (1961).