Esters, cleavage with iodotrimethylsilane

The ABC-ring carboxylic acid 17 and the FGH-ring alcohol 18 were connected under Yamaguchi conditions to give ester 19 (Scheme 28.3). Desilylation with tetra-n-butylammonium Fluoride (TBAF), acid-catalyzed acetal formation with y-methoxyallylstannane 20, and acetal cleavage with iodotrimethylsilane/hexamethyldisilazane prodnced (y-alkoxyallyl)stannane 21. The ester 21 was... 

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. 

Ester Cleavage. Although esters are readily cleaved with iodotrimethylsilane, reaction of esters with TMS-Br under similar conditions gives somewhat lower yields of silyl esters or acids upon hydrolysis (eq 4). Lactones, however, react with TMS-Br at 100 °C to afford < >-bromocarboxylic acids after hydrolysis of the silyl ester (eq 5). ... 

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... 

When exposed to iodotrimethylsilane at room temperature, 59 underwent C-O bond cleavage along with iodination to produce the silyl ester 60 (Fig. 11). In situ cyclization was carried out by treating 60 in methanol at room temperature to provide (+)-mono-morine I (62) and its C-3 epimer (63) in 42% and 40% yields from 59, respectively. An appreciable improvement of the diastereo-selectivity in the cyclization to monomorine I was obtained by the following sequence. With compound 59 in hand, the ketone 61 was prepared by Collins oxidation in 94% yield. On catalytic hydrogenation of 61, ( )-monomorine I (62) was obtained in 71% yield, along with ( )-3-epimonomorine I (63) as a minor isomer (15%). 

In Situ Generation of Iodotrimethylsilane. Of the published methods used to form TMSI in situ, the most convenient involves the use of TMSCl with Nal in acetonitrile. This method has been used for a variety of synthetic transformations, including cleavage of phosphonate esters (eq 23), conversion of vicinal diols to alkenes (eq 24), and reductive removal of epoxides (eq 25). ... 

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