Chromium amides

Cr aUcoxides [Cr(OR)2] are conveniently prepared by alcoholysis of chromium amides, for example [Cr N(SiMe3)2 2(THF)2]. The alkoxides with bulky substituents are appreciably soluble in organic solvents, but... 

Primary and secondary amines, double bonds, aldehydes, sulfides and certain aromatic and dihydroaroraatic systems are also oxidized by chromium VI reagents under standard hydroxyl oxidizing conditions. Amines are commonly protected by salt formation or by conversion to amides. Aldehydes and... 

Chromium aminocarbenes [39] are readily available from the reaction of K2Cr(CO)5 with iminium chlorides [40] or amides and trimethylsilyl chloride [41]. Those from formamides (H on carbene carbon) readily underwent photoreaction with a variety of imines to produce /J-lactams, while those having R-groups (e.g.,Me) on the carbene carbon produced little or no /J-lactam products [13]. The dibenzylaminocarbene complex underwent reaction with high diastereoselectivity (Table 4). As previously observed, cyclic, optically active imines produced /J-lactams with high enantioselectivity, while acyclic, optically active imines induced little asymmetry. An intramolecular version produced an unusual anti-Bredt lactam rather than the expected /J-lactam (Eq. 8) [44]. 

Photodriven reactions of Fischer carbenes with alcohols produces esters, the expected product from nucleophilic addition to ketenes. Hydroxycarbene complexes, generated in situ by protonation of the corresponding ate complex, produced a-hydroxyesters in modest yield (Table 15) [103]. Ketals,presumably formed by thermal decomposition of the carbenes, were major by-products. The discovery that amides were readily converted to aminocarbene complexes [104] resulted in an efficient approach to a-amino acids by photodriven reaction of these aminocarbenes with alcohols (Table 16) [105,106]. a-Alkylation of the (methyl)(dibenzylamino)carbene complex followed by photolysis produced a range of racemic alanine derivatives (Eq. 26). With chiral oxazolidine carbene complexes optically active amino acid derivatives were available (Eq. 27). Since both enantiomers of the optically active chromium aminocarbene are equally available, both the natural S and unnatural R amino acid derivatives are equally... 

Chromium(III) is a commonly-used crosslinker for preparing profile control gels with polymers having carboxylate and amide functionalities (la,b). Cr(III) is applied in many forms. For example, it can be used in the form of simple chromic salts of chloride and sulfate, or as complexed Cr(III) used in leather tanning (2), or as in situ generated Cr(III) from the redox reaction of dichromate and bisulfite or thiourea. The gelation rate and gel quality depend on which form of Cr(III) is used. 

Mori has reported that in the reaction of chromium carbene 25 with an alkyne containing a tethered 4-amidobutyne unit (26), a postulated vinylketene complex (27) is intercepted by nucleophilic amide attack, yielding a mixture of lactams (28 and 29).15 The expected naphthol 30 was also isolated in low yield. 

Benzocyclobutenone was first prepared from 1 -bromobenzocyclobutene by hydrolysis followed by chromium trioxide oxidation.3 More recent procedures involve hydrolysis of 1,1-dichloro- or 1,1-dimethoxybenzocyclobutene which in turn have been obtained through cycloaddition of the appropriate 1,1-disubstituted ethylenes to benzyne generated either from anthranilic acid through diazotization5 6 or from bromobenzene through sodium amide treatment.7.3 Benzocyclobutenone has... 

Stereoselective deprotonation of componnd 581 is possible (Scheme 233), bnt the yields and enantioselectivities obtained are poorer than for the chromium-complexed analogues (see below). With an internal electrophilic quench it was possible to form the axially chiral benzamide 582 in 89% ee using hthium amide 360 . 

Ethylene, aluminum catalyst A1PO-1, heptane, chromium(III) tris(bis(trimethyl-silyl)amide), nonane, chromium(III) tris(bis(trimethylsilyl)amide)... 

The reaction conditions of example 1 were repeated using a different hydrocarbyl aluminum activator in a 4 1 molar ratio to chromium(III) tris(bis(trimethylsilyl)-amide). Reactions were conducted at an ethylene pressure of 100 psi at 70°C for 60 minutes. Neither 1-butene nor 1-decene was detected in the product mixture. A summary of reaction scooping is provided in Table 1. 

Scheme 3.8 Metallation reactions of bis(benzene)chromium and bis(toluene)chromium with alkali metal alkyls and magnesium amides ...

VC13 with primary amines gave similar derivatives containing one coordinated amide and one or more molecules of amine,64 but ethylenediamine186,187 and propylenediamine186 give [V(L)3]C13 (L = en, pn). These are isomorphous with the chromium(III) complexes the chlorine atoms are ionic, and the cations are tris-bidentate. 

Some multinuclear chromium(III) complexes which contain pyridine ligands have been described. The amide (122 - FL,L) reacts with CrCl3-6H20 in pyridine solution containing Na2C03 to give the dimer [Cr2(HL)2(py)4]-2py, the structure of which is described in Section 35.4.2,11.519... 

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