[12110-37-1] · C13H8CrO3 · Tricarbonyl(naphthalene)chromium · (MW 264.21)
Physical Data: mp 150-160 °C.
Solubility: sol THF, acetone.
Form Supplied in: a red moisture-sensitive crystalline solid.
Preparative Method: prepared in 75-83% yield by treating naphthalene with Hexacarbonylchromium in dry decalin.1
Purification: recrystallized under nitrogen from petroleum ether.
Handling, Storage, and Precautions: should be handled under a nitrogen or argon atmosphere, and a glove box would be ideal. The solid should be stored at low temperature, in the dark, under nitrogen.
The title reagent (1) is an arene chromium complex which catalyzes the stereoselective hydrogenation of alkynes to the (Z)-alkene (in degassed THF) (eq 1).2
The title reagent has been reported to catalyze the 1,4-hydrogenation of a carbocyclic 1,3-diene, resulting in the stereospecific formation of an exocyclic (Z)-alkene in 95% yield (eq 2).3
The resulting exocylic carbocyclic alkene was used in the synthesis of carbacyclin. Use of (1) (20 mol %) in the 1,4-hydrogenation of a dienol acetate in the presence of hydrogen (eq 3) resulted in the stereospecific synthesis of a trisubstituted exocyclic (Z)-allylic acetate (87% yield).4 This intermediate was used in the synthesis of anthracycline analogs.
The use of (1) as a hydrogenation catalyst requires the use of polar coordinating solvents (THF or acetone) and degassing of the reaction mixture. Hydrogen or an inert gas is introduced into the reaction flask, depending on the substrate.
The title reagent will catalyze the rt isomerization of conjugated dienes, with complete control of the stereochemistry of the resulting alkene in the absence of any molecular hydrogen.4 The mechanism involves a stereo- and regiocontrolled 1,5-hydrogen shift of the (Z)-conjugated diene. Under very mild conditions the stereospecific isomerization of the diene occurs to give an exocylic (Z)-diene. Aromatization by means of mild oxidation results in the formation an aryl excocyclic (Z)-alkene (eq 4).5
Extension of this methodology to silyloxymethyl- (eq 5)6 and aminomethylbutadiene derivatives (eq 6)7 resulted in the stereocontrolled synthesis of (Z)-silyl dienol ethers and (Z)-dienamines. Yields are good to excellent (57-97%) and the resulting heteroatom-substituted butadienes have been successfully shown to undergo inter- and intramolecular Diels-Alder reactions.6,7
Adam A. Galan
Parke Davis Pharmaceutical Research Division, Ann Arbor, MI, USA