ca01 only detailed ToC 1..24

118 Science of Synthesis 2.6 Complexes of Cr, Mo, and W without CO Ligands
2.6.4.5.2 Variation 2:
Reaction of Organochromium(III) Compounds Prepared
from Chromium(II) Chloride by Oxidative Addition
(The Nozaki–Hiyama–Kishi Procedure)
This methodology was pioneered by Hiyama [126] and refined by Kishi [127] and Nozaki. [128]
The organochromium reagent is readily formed from chromium(II) salts upon one-electron
oxidative addition (Section 2.6.4.2.1) of a wide range of substrates including allyl,
propargyl, alkenyl, and aryl halides, alkenyl trifluoromethanesulfonates, and allyl sulfonates
and phosphates. The most convenient chromium(II) salt is the anhydrous chloride,
which can either be purchased or prepared in situ from chromium(III) chloride and various
reducing agents. The performance of the chromium(II) chloride reagent in forming
the Cr-C bond is enhanced by the addition of a catalytic amount of nickel(II) chloride.
[127,128]
The alkylchromium(III) species are highly aldehyde selective, e.g. the formation of 69
in Scheme 29. [126] The most important feature, however, is the unparalleled compatibility
with a wide array of functional groups in both reaction partners. In addition, the method
features useful stereoselectivities. Substituted allyl reagents lead to the homoallyl alcohols.
If the allyl reagent is ª-monosubstituted, the anti-alcohol is favored independent of
whether the starting halide is E or Z configured; see the synthesis of 70 where the antiproduct
is obtained in 100% selectivity. [129] Alkenyl halides or trifluoromethanesulfonates
react with complete retention of their double-bond geometry, e.g. the synthesis of 71. [128]
These useful features have made chromium-induced inter- or intramolecular C-C bond
formations a frequent key step in the total synthesis of molecules of utmost complexity,
[130] including the total synthesis of brevetoxin B. [131]
Scheme 29 The Nozaki–Hiyama–Kishi Reaction [126,128,129]
OHC
PhCHO +
Ph
OTf
O
Br
+ PhCHO
+
Br
CrCl3/LiAlH4 THF, rt
87% Ph
CrCl2, NiCl2 (cat.)
DMF, 25 oC 92%
CrCl 2 (1.2 equiv), THF
3,3,6-Trimethylhepta-1,5-dien-4-ol; Typical Procedure: [126]
CrCl 3 (4.28 g, 27 mmol) was reduced with LiAlH 4 (513 mg, 13.5 mmol) in THF (20 mL). After
stirring at rt for 10 min, 3-methylbut-2-enal (0.56 g, 6.1 mmol) and subsequently 1-bromo-
3-methylbut-2-ene (2.01 g, 13.5 mmol) in THF (10 mL) were added dropwise over 20 min.
Stirring for 3 h, followed by workup and distillation (97–100 8C/4 Torr, Kugelrohr), gave
the product as an oil; yield: 0.90 g (88%).
Ph
OH
70
HO
71
66%
Ph
OH
69
O