Page 937 - Advanced Organic Chemistry Part B - Reactions & Synthesis

metal–catalyzed reactions involve carbenoid intermediates in which the carbene is 913
bound to the metal. 146 The metals that have been used most frequently in synthetic
reactions are copper and rhodium, and these reactions are discussed in Section 10.2.3.2 SECTION 10.2
Reactions Involving
Carbenes and Related
10.2.2.2. Carbenes from Sulfonylhydrazones. The second method listed in Intermediates
Scheme 10.8, thermal or photochemical decomposition of salts of arenesulfonylhy-
drazones, is actually a variation of the diazoalkane method, since diazo compounds
are intermediates. The conditions of the decomposition are usually such that the diazo
compound reacts immediately on formation. 147 The nature of the solvent plays an
important role in the outcome of sulfonylhydrazone decompositions. In protic solvents,
the diazoalkane can be diverted to a carbocation by protonation. 148 Aprotic solvents
favor decomposition via the carbene pathway.
O H
base –
RCR +NH 2 NHSO Ar R C NNSO Ar R C N NSO Ar
2
2
2
2
2
– + hν
R C N NSO Ar R 2 C N N – R C:
2
2
2
H or Δ
+ SOH + +
R C N N – R C N N R CH +N 2
2
2
2
10.2.2.3. Carbenes from Diazirines. The diazirine precursors of carbenes
(Scheme 10.8, Entry 3) are cyclic isomers of diazo compounds. The strain of the small
ring and the potential for formation of nitrogen make them highly reactive toward loss
of nitrogen on photoexcitation. Diazirines have been used mainly in mechanistic inves-
tigations of carbenes. They are, in general, somewhat less easily available than diazo
compounds or arenesulfonylhydrazones. However, there are several useful synthetic
routes. 149
CH OR CH 2 OR
2
O 1) NH , N O
3
OMe OMe
O OR NH OSO H OR
3
2
N
2) I 2
R = TMS OR OR Ref. 150
NH 2 N
NaOCl, LiCl N
O C C CH O C
CH 3 2 3 2
Cl
NH Ref. 151
146
W. R. Moser, J. Am. Chem. Soc., 91, 1135, 1141 (1969); M. P. Doyle, Chem. Rev., 86, 919 (1986);
M. Brookhart, and H. B. Studabaker Chem. Rev., 87, 411 (1987).
147 G. M. Kaufman, J. A. Smith, G. G. Vander Stouw, and H. Shechter, J. Am. Chem. Soc., 87, 935 (1965).
148
J. H. Bayless, L. Friedman, F. B. Cook, and H. Shechter, J. Am. Chem. Soc., 90, 531 (1968).
149 For reviews of synthesis of diazirines, see E. Schmitz, Dreiringe mit Zwei Heteroatomen, Springer
Verlag, Berlin, 1967, pp. 114–121; E. Schmitz, Adv. Heterocycl. Chem., 24, 63 (1979); H. W. Heine, in
Chem. Heterocycl. Compounds, Vol. 42, Part 2, A. Hassner, ed., Wiley-Interscience, New York, 1983,
pp. 547–628.
150 G. Kurz, J. Lehmann, and R. Thieme, Carbohydrate Res., 136, 125 (1983).
151
D. F. Johnson and R. K. Brown, Photochem. Photobiol., 43, 601 (1986).