Chromium complexes imines

The intramolecular cyclization route to p-lactams still provides interest. P-Amino esters (obtained by a Reformatsky-type reaction of an imine and bromoacetates derived from chiral alcohols) are cyclized by the action Grignard reagents to 4-substituted P-lactams with impressive e.e. <96TL4095>. A similar approach through a Reformatsky-type reaction uses tricarbonyl(Ti -benzaldimine)chromium complexes and ultrasound <96T4849>. 3-Methyl-azetidin-2-ones (obtained from 3-amino-2-methylpropionates) have been resolved and their... 

The palladium-catalyzed trimethylenemethane reaction with tropanones was reported in 1987 by Trost and Seoane and is the first example of a [6 + 3]-cycloaddition.130 Chromium-mediated [6 + 3]-cycloadditions of two types have been described-one in which the chromium complex activates the six-carbon component and one in which the chromium complex activates the three-atom component. An example of the first type involves the reaction of a cycloheptatriene-Cr(CO)3 complex with azirines to give cyclic imines in moderate yields (Scheme 40).131... 

A further chiral auxiliary-based tactic exploited tricarbonyl( 76-arene)chromium complexes of aromatic imines 71, which reacted under ultrasound (US) irradiation with a-bromoesters in a predictable stereochemical course to give comparable amounts of /S-aminoesters and / -lactams, as outlined in equation 44127. Chromium decomplexation is eventually achieved by photochemical oxidation under air. 

Arene(tricarbonyl)chromium complexes, 19 Nickel boride, 197 to trans-alkenes Chromium(II) sulfate, 84 of anhydrides to lactones Tetrachlorotris[bis(l,4-diphenyl-phosphine)butane]diruthenium, 288 of aromatic rings Palladium catalysts, 230 Raney nickel, 265 Sodium borohydride-1,3-Dicyano-benzene, 279 of aryl halides to arenes Palladium on carbon, 230 of benzyl ethers to alcohols Palladium catalysts, 230 of carboxylic acids to aldehydes Vilsmeier reagent, 341 of epoxides to alcohols Samarium(II) iodide, 270 Sodium hydride-Sodium /-amyloxide-Nickel(II) chloride, 281 Sodium hydride-Sodium /-amyloxide-Zinc chloride, 281 of esters to alcohols Sodium borohydride, 278 of imines and related compounds Arene(tricarbonyl)chromium complexes, 19... 

In 2001, p-lactams have been reported to be obtained via Staudinger reaction with complete m-diastereoselection starting from prochiral imine chromium complexes (Scheme 14), [63]. 

Scheme 14 cw-Diastereoselective synthesis of (3-lactams using prochiral imine chromium complexes... 

Bis(phosphoranimine) ligands, chromium complexes, 5, 359 Bis(pinacolato)diboranes activated alkene additions, 10, 731—732 for alkyl group functionalization, 10, 110 alkyne additions, 10, 728 allene additions, 10, 730 carbenoid additions, 10, 733 diazoalkane additions, 10, 733 imine additions, 10, 733 methylenecyclopropane additions, 10, 733 Bisporphyrins, in organometallic synthesis, 1, 71 Bis(pyrazol-l-yl)borane acetyl complexes, with iron, 6, 88 Bis(pyrazolyl)borates, in platinum(II) complexes, 8, 503 Bispyrazolyl-methane rhodium complex, preparation, 7, 185 Bis(pyrazolyl)methanes, in platinum(II) complexes, 8, 503 Bis(3-pyrazolyl)nickel complexes, preparation, 8, 80-81 Bis(2-pyridyl)amines... 

Chromium complexes (continued) organohalide activation, 5, 381 with phosphine-based supporting ligands, 5, 365 porphyrin-ligated derivatives, 5, 364 pyridinebis(imine) ligand derivatives, 5, 361 salen-ligated complexes, 5, 379 surface chemistry on oxides, 12, 525 tetradentate [04] compounds, 5, 352 tetradentate thioether derivatives, 5, 365 thiolate-bridged, Fe- and Rh complexes, 5, 308 with Ti(IV), 4, 627... 

The photochemical generation of metal-bound ketenes from carbene-chromium complexes and the subsequent coupling with imines to give azetidin-2-ones is treated separately (Section 2.01.3.10.5). 

Imines with bulky groups at nitrogen give rise to the formation of fra r-azetidin-2-ones < 2000TL6551 >. Stereocontrolled syntheses have been carried out using chloral imines <2004TL6563>, tricarbonyl(7]6arene)chromium(0)complexed imines... 

The imine bond in 2-imidazolines reacts with Fisher carbenes under irradiation (Scheme 144). Low yields were obtained with monosubstituted imidazolines 608a-c due to thermal decomposition of the substrates under the reaction conditions. Optically active 4,4-disubstituted A -imidazolines 608d-e form azapenams (609d, 610e, 611) with (methoxymethylcarbene)chromium complex in good yields and high diastereoselectivity. The electronic nature of RVR clearly influences the sense of diastereoselectivity (609 vs. 610, 611) <1977JOC3586>. 

A chromium complex of benzaldehyde imine is also a good substrate for the Michael-type addition of organolithium reagents mediated by a stoichiometric amount of the chiral diether 6 in toluene to give the corresponding product in up to93%ee(Eq. (12.13)) [32]. 

An intramolecular reductive coupling of mono-chromium complexes of the biphenyls having carbonyl or imine groups at the both ortho-positions gave the trans-diolsy diamines or amino alcohols without formation of any stereoisomers (Eq.8) [8]. 

Similarly, the planar chiral tricarbonylchromium complexes of ortho substituted benzaldimines are useful for a variety of stereoselective cycloaddition reactions. For example, the benzaldimine chromium complexes gave aza-Diels-Alder product, 2,3-dihydro-4-pyridinone chromium complexes with high diastereoselectivity by reaction with Danishefsky s diene (Eq. 18) [11,17,18]. The high diastereoselectivity of the cycloadducts is also based on the preferred antz-conformation of the starting benzaldimine chromium complexes as well as the planar chiral benzaldehyde chromium complexes. The cycloaddition of imines having arene chromium complex at the remote position with Danishefsky s diene underwent smoothly in good yields, but the diastereoselectivity was low (Eq. 19) [17]. 

Similarly, ketene generated from acid chloride by treatment with triethyl-amine reacted with tricarbonylchromium-complexed benzaldimines to afford P-lactam derivatives via [2+2] cycloaddition with high diastereoselectivity. Thus, the cycloaddition of benzaldimine chromium complexes with ketenes generated from acid chloride at 0 °C in the presence of triethylamine afforded czs-p-lactam as a single diastereomer 27 (Eq. 20) [19]. Remote positioned imine having the planar chiral arene chromium complex was also reacted with ketene to afford p-lactam complex as diastereomeric mixture (Eq. 21) [19]. 

Chromium-complexed ketenes are obtained by irradiation of chromium aminocarbene complexes derived from chiral oxazolidines (CO pressure). These ketenes were found to react with imines diastereoselectively furnishing rram-P-lactams, exclusively. ... 

In an interesting and novel organometallic approach to monocyclic and bicyclic p-lactam synthesis, it has been shown that pentacarbonyl(methoxy-methyl)chromium complexes will add to imines under sunlight irradiation (Scheme 38). ... 

Silylketenes in formation of (3-lactones and (3-lactams 98JCS(P1)2105. Syntheses of (3-lactams, (3-lactones, and 1,3- and 1,4-diazetidinediones by pho-tochemically induced cycloaddition reactions of chromium carbene complexes with imines, aldehydes, and azo compounds 97T4105. 

A few heterocyclic imines reacted poorly if at all with chromium alkoxycarbene complexes. Oxazines required the use of the more reactive (and less stable) molybdenum alkoxycarbenes, producing oxacephams in -40% yield. Oxazo-lines gave low yields (-12%) of the oxapenam system, along with similar amounts of oxazinone, resulting from incorporation of two equivalents of ketene (Eq. 3) [20]. 

Other miscellaneous imines that underwent photoreaction with chromium alkoxycarbenes include iminodithiocarbonates [33],the mono-N-phenylimine of benzil and the bis-JV-phenyl imine of acetoin [20]. By preparing the chromium carbene complex from 13CO-labeled chromium hexacarbonyl, /J-lactams with two adjacent 13C labels were synthesized [34]. 

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]. 

Although the photodriven reactions of chromium carbene complexes with imines superficially resemble those of free ketenes, there are major differences. The optically active oxazolidine carbene (Table 5) gave excellent yields and high ee values when allowed to react with imidates, oxazines, thiazines, and... 

Lopez R, Sordo TL, Sordo JA, Gonzalez J (1993) J Org Chem 58 7036 Cossio F, Ugalde JM, Lopez X, Lecea B, Palomo C (1993) J Am Chem Soc 115 995 Cossio FP, Arrieta A, Lecea B, Ugalde JM (1994) J Am Chem Soc 116 2085 GerrietaA,Lecea B, Cossio FP (1998) J Org Chem 63 5869. For a theoretical treatment of the photoreaction of chromium carbene complexes with imines see Arrieta A, Cossio FP, Fernandez I, Gomez-Gallego M, Lecea B, Mancheno MJ, Sierra MA (2000) J Am Chem Soc 122 11509... 

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