TMSI

Trimethylsilyl iodide [16029-98-4] (TMSI) is an effective reagent for cleaving esters and ethers. The reaction of hexamethyldisilane [1450-14-2] with iodine gives quantitative conversion to TMSI. A simple mixture of trimethylchlorosilane and sodium iodide can be used in a similar way to cleave esters and ethers (8), giving silylated acids or alcohols that can be Hberated by reaction with water. 

ZnBr2, CH2CI2, 25°, 2-10 h, 90% yield. When a MEM-protected diol was cleaved using ZnBt2 EtOAc, 1,3-dioxolane formation occurred, but this can be prevented by the use of in situ-prepared TMSI. ... 

This group is stable to strong acids and bases, TMSI, Pd-C/H2, DDQ, TBAF, and LAH at low temperatures and thus has the potential to participate in a large number of orthogonal sets/... 

EtO)3SiCl, Nal, CH3CN, CH2CI2, —5°, 0.5 h, 74% yield. This method was reported to work better than TMSI. TBDPS groups were not affected by this reagent. 

ISiCl3, rt, 20-30 min, 74-95% yield. Esters and phenolic methyl ethers are reported to survive, whereas with the related TMSI they are cleaved. 

TMSI, In 5i7w-generated TMSI is also effective. 

It has been shown that TMSI is capable of mediating the reaction at room temperature. The classical three component coupling was carried out using aldehyde 82 and ketoester 83 with ammonium acetate in acetonitrile at room temperature with in situ generated TMSI. This gave a 73-80% yield of 1,4-dihydropyridines 84 in 6-8 h. The best results were obtained with 1 equivalent of TMSCl and 1 equivalent of Nal. 

The C-2 proton in an aziridine-2-carboxylate is acidic, due to the adjacent carboxylic group. Upon treatment with base, such aziridines may undergo ring-opening reactions to give a-amino-a, 3-unsaturated carboxylates [74, 94, 95]. As an example, treatment of 111 (Scheme 3.39) with TMSI/Et3N gave 116 in 64% yield [74]. 

TMSCN, TMSI, TMSN3 TMSSMe. W. C. Groutas and D. Felker, Synthesis 861 (1980). TMSI, TMSBr A. H. Schmidt, Aldrichimica Ada 14, 31 (1981). 

Trimethylsilyl iodide (TMSI) cleaves methyl ethers in a period of a few hours at room temperature.89 Benzyl and f-butyl systems are cleaved very rapidly, whereas secondary systems require longer times. The reaction presumably proceeds via an initially formed silyl oxonium ion. 

Allylic ethers are cleaved in a matter of a few minutes by TMSI under in situ conditions. 

TMSI also effects rapid cleavage of esters. The cleavage step involves iodide attack on the O-silylated ester. The first products formed are trimethylsilyl esters, but these are hydrolyzed rapidly on exposure to water.96... 

A number of related procedures have been developed. For example, TMSI can be used.181... 

Silylating reagents such as TMSI and TMS triflate have only a modest catalytic effect, but the still more powerful silylating reagent (CH3)3SiB(03SCF3)4 does induce addition to aldehydes.90... 

Materials. Methyl methacrylate was a product of Rohm and Haas, and t-butyl methacrylate was obtained from Polvsciences, Inc. Potassium trimethylsilanolate (PTMS) was obtained from Petrarch Systems, Inc. Anhydrous lithium iodide, trimethylsilyl iodide (TMSI), and n-butyllit.ium (in hexanes) were purchased from Aldrich Chemical Co. 

All other reagents and solvents were obtained from Kodak Laboratory Chemicals. All monomers were purified by distillation under an inert atmosphere. They were distilled from and collected over 3 A molecular sieves just prior to the polymerizations (11). TMSI was distilled under an inert atmosphere and stored over copper powder. 

Reaction of S-b-MM with Trimethylsilyl Iodide. The reaction was carried out under nitrogen in a 250-mL, round-bottom flask equipped with a magnetic stirrer. To a solution of S-b-MM-94/6-wt (5.01 g, 2.9 meq MM) in dichloromethane (50 mL) was added TMSI (1.3 g, 6.3 mmol) via syringe. The solution was refluxed for 22 hr. It was cooled, precipitated from methanol, washed with methanol, and dried, yielding 4.39 g. NMR, IR, and GPC analyses were virtually identical to those of the starting material. 

Reaction of S-b-tBM with Trimethylsilyl Iodide. The reaction was carried out under conditions similar to that employed for the reaction of S-b-MM with TMSI. A mixture of S-b-tBM-87/13-wt (10.0 g, 9.3 meq tBM) in dichloromethane (100 mL, dried over 3 A sieves) was treated with TMSI (5.0 g, 25 mmol) and was stirred for 4 hr at room temperature, resulting in a dark red solution. The solvent was partially evaporated, and the residue was precipitated from methanol. The precipitate was washed with several portions of methanol and was dried. It was redissolved in 1 9 water-THF (300 mL), 3 mL of cone. HC1 was added, and the mixture was refluxed for 2 hr. The solvents... 

A 0.42 g portion of the initial product from the reaction of MM-b-tBM with TMSI was converted to its potassium salt in the same manner as that previously described above for S-b-MA, yielding 0.20 g of MM-b-MA.K. Analyses IR (film) v 1729 and 1552 cm-1 ICP ... 

We next investigated the dealkylation of S-b-tBM with TMSI. Unlike the reaction with S-b-MM, it required only 4 hr at room temperature to completely cleave the t-butyl ester. Work-up under acidic conditions gave S-b-MA which was virtually identical by NMR, IR, GPC, and titration with that just described above. Likewise, neutralization with KOH resulted in quantitative conversion to S-b-MA.K. Although the initially formed product of the reaction of alkyl esters with TMSI is presumably the trimethylsilyl ester (1 7 ), we were not able to isolate or characterize this copolymer. It is known that trimethysilyl methacrylate and its polymers spontaneously hydrolyze even in moist air (19). Any traces of water in the methanol used to precipitate the reaction mixture would thus preclude isolation of the intermediate trimethylsislyl ester. 

The Preparation of MM-b-MA and MM-b-MA.K. Inspired by the unexpected selectivity of the reaction of TMSI with S-b-MM and S-b-tBM, we decided to attempt the preparation of poly(methyl methacrylate-b-t-butyl methacrylate) (MM-b-tBM) and its unprecedented conversion to MM-b-MA. 

Treatment of this polymer with TMSI under the same conditions employed for the reaction with S-b-tBM resulted in a quantitative production of MM-b-MA. The t-butyl signal in the NMR spectrum is now gone (Figure 3b), and the carbonyl band in the IR spectrum is further broadened and shifted to 1717 cm (Figure 4b). Titration for MA resulted in 0.583 meq COOH/g, in accord with the value of 0.56 meq/g calculated based on the amount of tBM present in the NMR spectrum. Conversion to the potassium methacrylate copolymer was straightforward. IR analysis of the product shows the carboxylate band at 1552 cm-1, and the ester band at 1729 cm-1 (Figure 4c). Assay for potassium (ICP) confirmed that the neutralization was quantitative. 

A more interesting reagent is TMSI. Although MM blocks are unreactive toward TMSI, tBM blocks are cleanly converted to MA blocks under very mild conditions. This chemoselectivity of TMSI has been exploited to prepare the novel block copolymers MM-b-MA and MM-b-MA.K. The tBM blocks can also be readily hydrolyzed with TsOH, corroborating previous reports of this transformation. 

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