Titanium bromide reduction

A third method for the synthesis of cycl[3.2.2]azines, from iV-(aroylmethyl)pyridinium salts via indolizines, involves intramolecular (reductive) McMurry coupling of the latter. For example, 3,5-dibenzoylindolizines, obtained from 2-benzoyl-iV-phenacylpyridinium bromide as shown (Scheme 91), are cyclized using zinc and titanium(iv) chloride to give the 3,4-diphenylcyclazines 352 in high yield (>90%). The reaction cannot be applied, however, to... 

It is remarkable that even cyclobutylmagnesium bromides react cleanly with titanium alkoxides to yield reactive titanacyclopropane intermediates that reductively cyclopropa-nate N,N-dialkylformamides. This constitutes the first synthesis of the highly strained N,N-dialkylbicyclo[2.1.0]pent-5-ylamines (Table 11.9, entries 29—31). 

Chlorophenyl)glutarate monoethyl ester 87 was reduced to hydroxy acid and subsequently cyclized to afford lactone 88. This was further submitted to reduction with diisobutylaluminium hydride to provide lactol followed by Homer-Emmons reaction, which resulted in the formation of hydroxy ester product 89 in good yield. The alcohol was protected as silyl ether and the double bond in 89 was reduced with magnesium powder in methanol to provide methyl ester 90. The hydrolysis to the acid and condensation of the acid chloride with Evans s chiral auxiliary provided product 91, which was further converted to titanium enolate on reaction with TiCI. This was submitted to enolate-imine condensation in the presence of amine to afford 92. The silylation of the 92 with N, O-bis(trimethylsilyl) acetamide followed by treatment with tetrabutylammonium fluoride resulted in cyclization to form the azetidin-2-one ring and subsequently hydrolysis provided 93. This product was converted to bromide analog, which on treatment with LDA underwent intramolecular cyclization to afford the cholesterol absorption inhibitor spiro-(3-lactam (+)-SCH 54016 94. 

In 1973, the direct potassium metal reduction of zinc salts was reported.3 This active zinc powder reacted with alkyl and aryl bromides to form the alkyl- and arylzinc bromides under mild conditions.4 The reduction of anhydrous zinc salts by alkali metals can be facilitated through the use of electron carriers. Lithium and sodium naphthalenide reduce zinc salts to give highly reactive metal powders under milder and safer conditions. Graphite5 and liquid ammonia6 have also been employed as electron carriers in producing zinc powders. A highly dispersed reactive zinc powder was formed from the sodium metal reduction of zinc salts on titanium dioxide.7... 

California Red Scale is a worldwide citrus pest which can be controlled by means of the pheromone 60. Cohen used reductive lithiation to generate versatile allylic nucleophiles applicable to this type of target.6 The allyl sulfide 61 is lithiated by BuLi and reacts with butenyl bromide a to sulfur to yield 63. Reductive lithiation (Li, DBB) of the product yields allyllithium 64. A regioselective reaction of this nucleophile with formaldehyde at the more substituted terminus is ensured by transmetallation to the allyl titanium 65, which gives 66 after treatment with formaldehyde and bromination. 

The mixed cyclopentadienyl-cycloheptatrienyl ( 5-7 ) titanium complex Cp( -C7H7)Ti has been prepared in 33 -40% yield by the reduction of CpTiCb with isopropylmag-nesium bromide or Mg in the presence of cycloheptatriene. Reduction of Cp TiCb in THF with Mg in the presence of cycloheptatriene gives Cp ( -C7H7)Ti in 68% yield. Titanium 5-7 complexes exhibit sandwich structures see Sandwich Compound) with the five-membered and seven-membered rings nearly parallel to each other. 

Reduction of aryl bromides with lithium aluminum hydride takes place in tetrahydrofuran solutions at room temperature. It has also been performed with bener results in the presence of di-r-butyl peroxide under UV irradiation or in the presence of titanium tetrachloride (equations 56 and 57). Reduction of bromobenzene with sodium bis(methoxyethoxy)aluminum hydride (Red-Al, Vitride) at 100-115 C gives benzene in 53% yield (Table 4). ... 

Intermolecular cyclization of 4-dialkylamino-2-aza-l,3-diene-1,1-dicarbonitriles proceeds on treatment with hydrogen bromide in acetic acid to yield 2-bromo-3-cyanopyrazine <90HCA1210>. Tetraalkyl or -arylpyrazines are synthesized by reductive cyclization of the corresponding nitriles with titanium tetrachloride and zinc in modest to good yields (Equation (18)) <90S70l>. 

The present preparation Illustrates a general and convenient method for a two-step deoxygenation of carbonyl compounds to olefins. Related procedures comprise the basic decomposition of p-toluenesulfonylhydrazones,2 the hydride reduction of enol ethers,3 enol acetates,9 enamines,3 3 the reduction of enol phosphates (and/or enol phosphorodlamidates) by lithium metal in ethylamine (or liquid ammonia),33 the reduction of enol phosphates by titanium metal under aprotic conditions,32 the reduction of thioketals by Raney nickel,33 and the reduction of vinyl sulfides by Raney nickel in the presence of isopropylmagnesium bromide.3 ... 

Reduction of bromides. In the presence of catalytic amounts of this or-ganometallic reagent, isopropylmagnesium bromide reduces vinyl, aryl, and alkyl bromides in ether at 20°. Chlorides are not reduced by this system thus p-bromochlorobenzene can be reduced to chlorobenzene in almost quantitative yield. The titanium hydride Cp2Ti—H is considered to be involved. 

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