Chromium trimethylsilyl chloride

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]. 

Optically active (—)-(8R)-methylcanadine was stereoselectively synthesized through selective monocomplexation of (—)-canadine (26) to chromium tricarbonyl (240). Heating of chromium hexacarbonyl with 26 effected regioselective complexation of the D ring to give the diastereomeric complexes, which were treated with n-butyllithium and trimethylsilyl chloride to give the 11-trimethylsilyl derivative 475 (Scheme 97). Methylation of this complex with methyl iodide gave stereoselectively the 8-methyl derivative 476 by preferential alkylation from the opposite face to the bulky chromium... 

The mixture of chromium trioxide with one equivalent of trimethylsilyl chloride, with no solvent added, results in the formation of an explosive red liquid that is soluble in dichloromethane or tetrachloromethane.428 It is suggested, with no spectroscopic evidence, that it consists of trimethylsilyl chlorochromate [Me3Si-0-Cr(0)2-Cl]. This compound, which can safely be used in organic solvents, is able to oxidize alcohols to aldehydes or ketones, and interacts with r-butyldimethylsilyl ethers producing deprotection, followed by oxidation of the liberated alcohol.138 Compounds analogue to trimethylsilyl chlorochromate are also able to oxidize alcohols, although they possess lesser reactivity. They can be prepared by reaction of chromium trioxide with dimethyldichlorosilane and diphenyldichlorosilane.428b... 

Trimethylsilyl chlorochromate (19) must be formed in situ from trimethylsilyl chloride and moist, powdered chromium(VI) oxide, since attempted isolation results in explosions. 

N-Chlorocarbamate/Chromium(II) Chloride. Enol ethers (see Eq. 80) and glycals (see Eq. 84) react with N-chlorocarbamates in the presence of chromous chloride to produce a-amino carbonyl derivatives.343 Trimethylsilyl enol ethers give low yields because of their ease of hydrolysis. A radical chain mechanism has been proposed with the N-haloamide acting as the transfer agent (Eq. 32).344... 

The Nozaki-Hiyama-Kishi (NHK) reaction involves the mild addition of chro-mium(II) organometallics to aldehydes to give homoallylic alcohols in a regio- and stereo-controlled fashion.111 A very significant achievement in the chromium organometallic chemistry was accomplished by Fiirstner who developed a catalytic version of the NHK reaction based on the coupled use of the redox Mn(0)/Cr(III) couple and trimethylsilyl chloride (TMSC1).[21 Moreover, the integration of the Fiirstner protocol with the addition of the Jacobsen s Salen /V,/V -bis(3,5-di-f-butylsalicylidene)-l,2-cyclohexanediamine] and triethylamine allowed Cozzi, Umani-Ronchi, et al. to develop a catalytic enantioselective route to homoallylic alcohols.[3]... 

Catalysed aerobic epoxidation of the styrene-cobalt complex, followed by the addition of trimethylsilyl isothiocyanate, yields 4-phenyloxazolidine-2-thione 123 <96TL7315>. The 4-substituted 2-oxazolidinone 124 undergoes a "chromium Reformatsky" reaction with aldehydes RCHO (R = i-Pr or Ph) in the presence of chromium(ll) chloride and lithium iodide to give mainly the unusual anti-aldol products 125 in excellent dia,stereomeric excess and yield <97TL4,387>. 

Chromium trioxide j trimethylsilyl chloride 2-Cyanopyridinium chlorochromate a-Chloroketones from ethylene derivs. 

Chromium carbenes can also be prepared by the so-called Semmelhack-Hegedus route. Chromium hexacarbonyl is first reduced to a nucleophilic pentacarbonyl dichromate dianion 23 with sodium naphthalenide or potassium carbide. Reaction of this dianion species with an acid chloride gives a metal alkoxide that can be quenched with an electrophile to provide the desired chromate ester 24. Alternatively, the dianion can be added to an amide carbonyl to give a tetrahedral intermediated which collapses to the chromate amide 25 on treatment with trimethylsilyl chloride. 

Hydridocarbenes 8.19 are not available by this route. They can be prepared from formamides by reaction with the highly nucleophilic pentacarbonylchromium dianion 8.15, itself prepared by reduction of chromium hexacarbonyl with potassium/graphite (Scheme 8.4). The oxygen atom of the adduct 8.16 is removed using two equivalents of trimethylsilyl chloride. 

A complex formed from a chiral sulfonamide, chromium tribromide, Fe(tmhd)3, triethylamine, and manganese catalyzes the enantioselective allylation of aldehydes with 3-bromo-2-halopropenes in the presence of trimethylsilyl chloride and 2,6-lutidine (Scheme 4-319). The yields are in general good and the products are obtained with... 

Using chromium-based oxidants 2,4-Dimethylpentane-2,4-diol chromate(VI) diester, 122 Trimethylsilyl chlorochromate, 327 Using other oxidizing agents Bis(tributyltin) oxide, 41 Hydrogen hexachloroplatinate(IV)-Copper(II) chloride, 145 4-Methoxy-2,2,6,6-tetramethyl-1 -oxopiperidinium chloride, 183 Osmium tetroxide, 222 Potassium nitrosodisulfonate, 258 Samarium(II) iodide, 270 From alkenes by addition or cleavage reactions... 

Trimethylsilyldiazomethane, 327 Silyl substituted arenes Bis(trimethylsilyl)acetylene, 97 Chromium carbene complexes, 82 Titanium(IV) chloride-Diethylalu-minum chloride, 309 Other organosilanes Osmium tetroxide-Trimethylamine N-oxide-Pyridine, 223 Tributyltin chloride, 315 Di- x-carbonylhexacarbonyldicobalt, 99 Trimethylsilyl trifluoromethanesul-fonate, 329... 

Tricarbonyl(naphthalene)chromium, 19 Trimethylsilyl chlorochromate, 327 Cobalt Compounds Acylcobaltate complexes, 101 [Bis(salicylidene-y-iminopropyl)methyl-amine]cobalt(II), 41 Cobalt(II) chloride, 249 Cobalt zeolites, 296 Dicarbonylcyclopentadienylcobalt, 96 Di- x-carbonylhexacarbonyldicobalt,... 

In a similar fashion, chromium tricarbonyl complexes of aryl ketones are exclusively alkylated and reduced from the exo face relative to the metal. For example, addition of vinyl magnesium chloride to the substituted tetralone complex (42) affords the alcohol (43) exclusively with an antirelationship between the incoming nucleophile and the chromium tricarbonyl group (Scheme 83). This was used in a synthesis of 11-epi-helioporin B. 2-Trimethylsilyl-substituted benzaldehyde complexes undergo an interesting... 

Iodine, 72, 293-295, 333, 452,579 Iodine-Dimethyl sulfoxide, 295 Iodine-Potassium iodate, 296 Iodine-Pyridine N-oxide, 296 lodine-Pyridine-Sulfur dioxide, 296 Iodine azide, 297 Iodine bromide, 297 lodoacetonitrile, 494 a-lodo acyl chlorides, 116 o-Iodoanisole, 130 lodobenzene, 130, 443 7r-(Iodobenzene)chromium tricarbonyl, 104 lodobenzene diacetate-Trimethylsilyl azide, 297... 

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