Acetals iodotrimethylsilane

Likewise, synthetic 2//-azepines isomerize to 3//-azepines in refluxing chloroform (2-3 h) or in tert-butyl methyl ether at room temperature.291 The isomers can be readily separated by chromatography on silica gel, as the more basic 2//-azepines30 have lower Rf values. In contrast, 7-butyl-2//-azepin-2-acetic acid (11), obtained by heating the tert-butyl ester 10 with iodotrimethylsilane, is stabilized by intramolecular hydrogen bonding and shows no tendency to rearrange to the 3//-isomer.291... 

Alkyl esters are efficiently dealkylated to trimethylsilyl esters with high concentrations of iodotrimethylsilane either in chloroform or sulfolane solutions at 25-80° or without solvent at 100-110°.Hydrolysis of the trimethylsilyl esters serves to release the carboxylic acid. Amines may be recovered from O-methyl, O-ethyl, and O-benzyl carbamates after reaction with iodotrimethylsilane in chloroform or sulfolane at 50—60° and subsequent methanolysis. The conversion of dimethyl, diethyl, and ethylene acetals and ketals to the parent aldehydes and ketones under aprotic conditions has been accomplished with this reagent. The reactions of alcohols (or the corresponding trimethylsilyl ethers) and aldehydes with iodotrimethylsilane give alkyl iodides and a-iodosilyl ethers,respectively. lodomethyl methyl ether is obtained from cleavage of dimethoxymethane with iodotrimethylsilane. 

Acenaphthylene, 58, 73 Acetaldehyde, 58, 157 Acetals, cleavage with iodotrimethylsilane, 59, 40... 

Iodomethyltrimethylsilane, 315 Iodotrimethylsilane, 329 Ketene alkyl trialkylsilyl acetals or ke-tals, 19, 237, 306, 307, 351 Ketene f-butyl t-butyldimethylsilyl acetal, 237... 

Few examples of intramolecular enol silyl ether or silyl ketene acetal cyclizations to oc,3-enones have been reported. Notable, as exemplified in Scheme 34, is the iodotrimethylsilane-mediated intramolecular cyclization of 5-(iodoacetoxy)-a,3-enones (211) to 5-lactones (214). These cyclizations proceed with in situ generated silyl ketene acetals (212) arising from iodotrimethylsilane reduction of the iodoacetoxy moiety.87... 

Cleavage of ethers. The actual reagent formed from these two reagents is believed to be iodotrichlorosilane and is similar to iodotrimethylsilane for cleavage of ethers but somewhat more regioselective. It also cleaves acetals and ketals quantitatively to the carbonyl compound at room temperature. 

Thus two successive oxidations of 429 (Scheme 59) involving the Jones reagent and dichlorodicyano-p-benzoquinone respectively led to the enone 430. A similar reductive cleavage as above of the derived dimethyl acetal 431 with diisobutylaluminium hydride occurred from the less hindered a-side to furnish the P-methoxyether 432 as the major isomer. Selective O-debenzylation of432, achieved with iodotrimethylsilane led to ( )-coccinine (413). 

The acetal 14, activated by the iodotrimethylsilane 17, produces the oxonium cation 16 which can be intercepted by allylsilane 1 yielding homoallylic ether 15, one equivalent of methoxytrimethylsilane 18 and the catalyst 17. 

At the end of his review [7] dealing with the acetalization of carbonyl compounds, Sakurai reported a previously unpublished observation. In the presence of catalytic amounts of iodotrimethylsilane and one equivalent of tetramethoxysilane 38, allyl-trimethylsilane 1 underwent smooth condensation with benzaldehyde 39, leading to adduct 41 in good yield. The silyl-modified Sakurai reaction was born (Scheme 13.15). 

Recent methods for the cleavage of allyl ethers that have that have yet to be tested on the anvil of complex target synthesis include (a) diborane generated in situ by reaction of sodium borohydride with iodine in THF at 0 °C (cyanoT ester, nitro, acetonide and tetrahydropyranyl groups survive) 434 (b) cerium(Ill) chloride and sodium iodide in refluxing acetonitrile (benzyl. THP and Boc groups survive) 435 (c) iodotrimethylsilane in acetonitrile at room temperature 436 and (d) DDO in wet dichloromethane (secondary allyl ethers, benzyl, acetate and TBS groups survive).437... 

Acetaliziation and aUylation of carbonyl compounds Iodotrimethylsilane is an effective catalyst for acetalization with an alkoxysilane. Addition of allyltrimethylsilane to this reaction results in allylation of the acetal to form a homoallyl ether. 

Sakurai, H., Sasaki, K., Hosomi, A. Chemistry of organosiiicon compounds. 143. Regiospecific aiiyiation of acetals with aiiyisiianes catalyzed by iodotrimethylsilane. Synthesis of homoallylethers. Tetrahedron Lett. 1981, 22, 745-748. 

HomoallyUc ethers.1 Iodotrimethylsilane catalyzes the allylation of acetals and ketals by allylsilanes, with transposition of the allylic group (equation I). It does not catalyze allylation of aldehydes and ketones. Note that TiCI4 can catalyze both of these reactions (7, 370-371). In this respect, ISi(CH3)3 resembles (CH3)3SiOTf (this volume). 

Deoxygenation of aieohols and ethers. Treatment of alcohols and methyl or trimethylsilyl ethers in acetonitrile with this iodotrimethylsilane equivalent and then zinc (previously activated with aqueous hydrochloric acid) and a little acetic acid results in deoxygenation to alkanes, usually in 60-90% yield. Presumably an alkyl iodide is an intermediate. 

The C 0 bonds of ethers, acetals, and esters are cleaved with iodotrimethylsilane (eq (39)) [36]. Various halosilanes, silylamines, and N,0-bis(trimethylsilyl)acetamide are used not only for the protection of alcohols, amines, and carboxylic acids but also for the conversion of them to the volatilizable compounds for GC analysis (eq (40)) [37]. Silyltriflates act as silating agents as well as Lewis acids (eq (41)) [38]. 

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