ca01 only detailed ToC 1..24

100 Science of Synthesis 2.6 Complexes of Cr, Mo, and W without CO Ligands
tional group tolerance and relatively low sensitivity to air, moisture, or solvent impurities.
[47] The process has proven particularly useful for the formation of cyclic ethers, e.g.
27. [48] A number of functional groups, including tertiary alcohols, do not interfere with
the course of the reaction. Amine and amide functional groups can be tolerated if they
cannot form unreactive chelated adducts for steric reasons. [49] A variant of this method
follows the initial ring-closing metathesis step with a carbonyl alkenation process, e.g.
the synthesis of 28, [50] which is, however, stoichiometric in metal because of the formation
of a catalytically inactive metal–oxo byproduct. The success of this strategy rests on
the fact that compound 26 metathesizes alkenes more rapidly than it alkenates ketones.
Chiral analogues of 26 have been prepared using C 2 symmetric diol ligands, and these
complexes, 29 [51] and 30, [52] have been used to perform the asymmetric ring-closing metathesis
of dienes [52–54] and the synthesis of chiral furans via enantioselective desymmetrization
reactions. [55]
Scheme 11 Cycloalkenes by Ring-Closing Metathesis of Dienes [48,50]
[M ]
X X
O
F 3C
F 3C
O
O
Ph
Ph
25
Pri N Pri O
CF3
Mo
O CHCMe2Ph CF3
29
+ H2C CH 2
Pr i
N Pri (F3C) 2MeCO
Mo
(F3C) 2MeCO CHCMe2Ph 26 (cat.)
benzene, 20 oC, 15 min
Pr i
92%
N Pri (F3C) 2MeCO
Mo
(F3C) 2MeCO CHCMe2Ph
26
benzene, 20 oC, 30 min
84%
Pri But O
O
Bu t
O Ph
27
O
28
N Pri Mo
CHCMe2Ph 1-[(2-Methyl-3-phenylallyl)oxy]methylcyclohex-1-ene (28); Typical Procedure: [50]
1-[(2-Methyl-3-phenylallyl)oxy]oct-7-en-2-one (35 mg, 0.13 mmol) was added to a homogeneous
yellow soln of catalyst 26 (100 mg, 0.13 mmol) in anhyd benzene (12 mL) under argon.
The resulting mixture was stirred at 20 8C for 30 min, at which time TLC showed the
reaction to be complete. The mixture was quenched by exposure to air, concentrated, and
30
Ph