Addition of Organochromium Reagents to Carbonyl Compounds

Abstract

Organochromium compounds can be prepared by two methods: (1) transmetallation from the corresponding organolithium, ‐magnesium, or –zinc compounds with chromium(III) halides, and (2) reduction of organic substrates, such as halides and unsaturated compounds with chromium(II) salts. The second method is usually the one ised because the first method suffers from low solubility of chromium(III) salts in ethereal solvents and from the difficulty of preparing organolithium compounds. Low‐valent chromium species are reducing agents. Reduction of various types of organic halides and compounds having unsaturated hetero‐hetero bonds with the chromium (II) species is discussed. Also described are the transmetallation to organochromium compounds from other organometallics, the nature of the carbon‐chromium bonds, and the X‐ray structure of chromium compounds. Reactions of organochromium reagents with carbonyl compounds and their scope and limitations are described. Included in this discussion are the geminal chromium reagents. Other reagents discussed are the chromium‐nickel compounds and alkylchromium and other organochromium reagents.

Harnessing the Power of the Water‐Gas Shift Reaction for Organic Synthesis

“…An example is represented by the allylation under Nozaki–Hiyama–Kishi/Fürstner conditions, which combines catalytic amounts of CrCl 2 (or CrCl 3 ) and superstoichiometric amounts of Mn. [201] Although catalytic in the metal that carries out the allylation reaction itself, protocols of this kind are de facto not catalytic, because a stoichiometric amount of metal reducing agent is still required. Truly catalytic methods include the transfer hydrogenation approach described by Krische.…”

The McMurry Coupling and Related Reactions

“…310 A marked advantage of this carbonyl olefination over the McMurry coupling is that the chromium reagents show high chemoselectivity toward aldehydes, and can be carried out in the presence of keto and ester functionalities.…”

Trace Amounts of Second Metal Elements Can Play a Key Role in the Generation of Organometallic Compounds

“…To tell the truth, I did not think at that time that the result of the reaction would initiate a new field of organochromium reagents and result in a review in Organic Reactions. 13 Further experiments revealed that reduction of alkenyl and aryl iodides (or bromides) to alkenyl-and arylchromium reagents with chromium(II) chloride and subsequent Barbiertype carbonyl addition proceeded smoothly. The reaction occurred in a stereoselective manner.…”

“…13,32,34 1.3 Geminal Dimetallic Reagents for Olefination of Carbonyl Groups: Organotitanium Reagents.…”

“…77 InCl 3 could be used instead of the indium(0) in this reaction. The 1 H and 13 C NMR spectra of the prepared allylaluminum solution in THF-d 8 revealed two sets of allyl peaks, suggesting the allylaluminum sesquibromide (allyl) 3 Al 2 Br 3 was formed ( Figure 11).…”