Page 359 - Advanced Organic Chemistry Part B - Reactions & Synthesis

-Fluoroketones are made primarily by reactions of enol acetates or silyl 331
enol ethers with fluorinating agents such as CF OF 129 , XeF , 130 or dilute
3
2
F . 131 Other fluorinating reagents that can be used include N-fluoropyridinium SECTION 4.3
2
salts, 132 1-fluoro-4-hydroxy-1,4-diazabicyclo[2.2.2]octane, 133 and 1,4-difluoro-1,4- Electrophilic Substitution
to Carbonyl Groups
diazabicyclo[2.2.2]octane. 134 These reagents fluorinate readily enolizable carbonyl
compounds and silyl enol ethers.
O O
+
PhCCH CH + F N + N OH PhCCHCH 3
2
3
88% Ref. 135
F
The -halogenation of acid chlorides also has synthetic utility. The mechanism
is presumed to be similar to ketone halogenation and to proceed through an enol. The
reaction can be effected in thionyl chloride as solvent to give -chloro, -bromo, or
-iodo acyl chlorides, using, respectively, N-chlorosuccinimide, N-bromosuccinimide,
or molecular iodine as the halogenating agent. 136 Since thionyl chloride rapidly converts
carboxylic acids to acyl chlorides, the acid can be used as the starting material.
N-chlorosuccinimide
CH (CH ) CH CO H CH (CH ) CHCOCI
3
2 3
3
2 3
2
2
SOCl 2
Cl
87%
I 2
PhCH CH CO H PhCH CHCOCl
2
2
2
2
SOCl 2
I 95%
Direct chlorination can be carried out in the presence of ClSO H, which acts as a strong
3
acid catalyst. These procedures use various compounds including 1,3-dinitrobenzene,
chloranil, and TCNQ to inhibit competing radical chain halogenation. 137
Cl , ClSO H
3
2
140°C
) CHCHCO H
(CH ) CHCH CO H (CH 3 2 2
3 2
2
2
chloranil
Cl
4.3.2. Sulfenylation and Selenenylation to Carbonyl Groups
The -sulfenylation 138 and -selenenylation 139 of carbonyl compounds are
synthetically important reactions, particularly in connection with the introduction of
129
W. J. Middleton and E. M. Bingham, J. Am. Chem. Soc., 102, 4845 (1980).
130 B. Zajac and M. Zupan, J. Chem. Soc., Chem. Commun., 759 (1980).
131
S. Rozen and Y. Menahem, Tetrahedron Lett., 725 (1979).
132 T. Umemoto, M. Nagayoshi, K. Adachi, and G. Tomizawa, J. Org. Chem., 63, 3379 (1998).
133 S. Stavber, M. Zupan, A. J. Poss, and G. A. Shia, Tetrahedron Lett., 36, 6769 (1995).
134
T. Umemoto and M. Nagayoshi, Bull. Chem. Soc. Jpn., 69, 2287 (1996).
135 S. Stavber and M. Zupan, Tetrahedron Lett., 37, 3591 (1996).
136 D. N. Harpp, L. Q. Bao, C. J. Black, J. G. Gleason, and R. A. Smith, J. Org. Chem., 40, 3420 (1975);
Y. Ogata, K. Adachi, and F.-C. Chen, J. Org. Chem., 48, 4147 (1983).
137
Y. Ogata, T. Harada, K. Matsuyama, and T. Ikejiri, J. Org. Chem., 40, 2960 (1975); R. J. Crawford, J.
Org. Chem., 48, 1364 (1983).
138 B. M. Trost, Chem. Rev., 78, 363 (1978).
139
H. J. Reich, Acc. Chem. Res., 12, 22 (1979); H. J. Reich, J. M. Renga, and I. L. Reich, J. Am. Chem.
Soc., 97, 5434 (1975).