Silyl iodide, hydrolysis

A number of approaches have been tried for modified halo-de-diazoniations using l-aryl-3,3-dialkyltriazenes, which form diazonium ions in an acid-catalyzed hydrolysis (see Sec. 13.4). Treatment of such triazenes with trimethylsilyl halides in acetonitrile at 60 °C resulted in the rapid evolution of nitrogen and in the formation of aryl halides (Ku and Barrio, 1981) without an electron transfer reagent or another catalyst. Yields with silyl bromide and with silyl iodide were 60-95%. The authors explain the reaction as shown in (Scheme 10-30). The formation of the intermediate is indicated by higher yields if electron-withdrawing substituents (X = CN, COCH3) are present. In the opinion of the present author, it is likely that the dissociation of this intermediate is not a concerted reaction, but that the dissociation of the A-aryl bond to form an aryl cation is followed by the addition of the halide. The reaction is therefore mechanistically not related to the homolytic halo-de-diazoniations. 

The carboxyl-based TL 1.43 (101) was easily prepared from hydroxymethyl PS resin and a trisubstituted aromatic compound its SP fimctionahzation on the amide carbonyl or on the chlorine atom is followed by cleavage with TMSl (trimethyl silyl iodide) for 72 h at 75 °C to obtain simultaneously ester hydrolysis and decarboxylation to 2-unsubstituted quinazolines. An expansion to other heterocyclic systems is easily foreseeable. 

On the other hand, hydrolysis with aqueous alkalis is complete, producing hydrogen and silicates. Silyl iodide gives a Wurtz-type reaction with sodium, wliich affords a useful path to disilane ... 

Miki and Hachiken reported a total synthesis of murrayaquinone A (107) using 4-benzyl-l-ferf-butyldimethylsiloxy-4fT-furo[3,4-f>]indole (854) as an indolo-2,3-quinodimethane equivalent for the Diels-Alder reaction with methyl acrylate (624). 4-Benzyl-3,4-dihydro-lfT-furo[3,4-f>]indol-l-one (853), the precursor for the 4H-furo[3,4-f>]indole (854), was prepared in five steps and 30% overall yield starting from dimethyl indole-2,3-dicarboxylate (851). Alkaline hydrolysis of 851 followed by N-benzylation of the dicarboxylic acid with benzyl bromide and sodium hydride in DMF, and treatment of the corresponding l-benzylindole-2,3-dicarboxylic acid with trifluoroacetic anhydride (TFAA) gave the anhydride 852. Reduction of 852 with sodium borohydride, followed by lactonization of the intermediate 2-hydroxy-methylindole-3-carboxylic acid with l-methyl-2-chloropyridinium iodide, led to the lactone 853. The lactone 853 was transformed to 4-benzyl-l-ferf-butyldimethylsiloxy-4H-furo[3,4- 7]indole 854 by a base-induced silylation. Without isolation, the... 

Reductive coupling of carbonyls to alkenes Titanium(IV) chloride-Zinc, 310 of carbonyls to pinacols Titanium(III) chloride, 302 Titanium(IV) chloride-Zinc, 310 of other substrates Samarium(II) iodide, 270 Reductive cyclization 2-(Phenylseleno)acrylonitrile, 244 Tributylgermane, 313 Tributyltin hydride, 316 Triphenyltin hydride, 335 Trityl perchlorate, 339 Reductive hydrolysis (see Hydrolysis) Reductive silylation Chlorotrimethylsilane-Zinc, 82... 

Fraser-Reid s stereocontrolled synthesis of the Woodward reserpine precursor 195 relied upon a tandem 5-exol6-exo radical cyclization of pyranose-derived dienes [76-77]. As outlined in Scheme 36, a,P-unsaturated ester 188 was prepared by free radical coupling of iodide 187 with a tin acrylate. After hydrolysis of 188 (MeONa, MeOH, 100%) to give primary alcohol 189, the silicon tethered diene 190 was installed by silylation. Treatment of 190 with n-BujSnH led to the desired cage molecule 192 in high yield via a 5-exo-trig cyclization to intermediate 191 followed by a 6-exo cyclization. Tamao oxidation of tricycle 192 led to diol... 

Corriu and coworkers found that the reaction of (Z)-y-Af,lV-bis(trhnethylsilyl)amino-1-propenylstannane 298 with butyllithium, followed by quenching with methyl iodide and then hydrolysis, provided 3-methylamino-l-propenylsilane 299 in high yield (equation 185)446, suggesting an anionic 1,4-silyl migration from N to C in the (Z)-vinyllithium 300 to give 301 (equation 186). The transmetallation of the ( )-isomer of 298 gave no silyl migration products (equation 187)447. 

Fig (19) Octalin ketal (163) is converted to kete dithioacetal (164) by the cleavage of ketal function and condensation with carbon disulfide and methyl iodide. Subjection of (164) to the action of dimethylsulfonium niethylide and acid hydrolysis leads to the formation of unsaturated lactone (165).lts furan silyl ether derivative is caused to undergo Diets-Atder reaction with methyl acrylate to obtain salicyctic ester (166) which is converted by standard organic reactions toabietane ether (167). It is converted to aiiylic alcohol (168) by epoxidation and elimination. Alcohol (169) obtained from (168) yields orthoamide which undergoes transformation to amide (170). Its conversion to the previously reported intermediate has been achieved by epoxidation, elimination and hydrolysis. 

The first examples of asymmetric Heck cyclizations that form quatemaiy carbon centers with high enantioselectivity came from our development of an asymmetric synthesis of the pharmacologically important alkaloid (—)-physostigmine (184) and congeners (Scheme 6-31) [68]. In the pivotal reaction, (Z)-2-butenanilide iodide 182 was cyclized with Pd-(5)-BINAP to provide oxindole 183 in 84% yield and 95% ee after hydrolysis of the intermediate silyl enol ether. With substrates of this type, cyclizations in the presence of halide scavengers took place with much lower enantioselectivity [68]. 

After a-metalation, methoxyallene was alkylated with bromo silyl ether 47 to afford 48. A second metalation at the terminus of the allene was quenched sequentially with carbon dioxide and methyl iodide to give the corresponding allenic ester. Hydrolysis of the enol ether and equilibration gave solely the (E)-y-keto acrylate 49 in 30% overall yield. Ketalization then provided 16, which had previously been converted to pyrenophorin (9). ° ... 

The synthesis of this special type of metallo-silanol starts most efficiently with an appropriate silyl metal complex, such as Cp(OC)2Fe-SiMe2R (R = H, OMe). An anionic shift of the silyl group from the iron to the cyclopentadienyl unit can be induced with lithium diisopropylamide, leading to the metallates 21a,b. Methylation with methyl iodide produces the neutral methyl iron complexes (C5H4SiMe2R)(OC)2Fe-Me (R = H, OMe), which can be converted either, for R = H, by the Co2(CO)8 method, or, for R = OMe, by hydrolysis in the presence of acetic acid, into the corresponding silanol 22. 

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