Methy silyl

In order to obtain further insight into the mechanism of the Mannich-type reaction, sulfone IP and silyl enol ether derived from acetophenone were reacted in the presence HOTf or TMSOTf, which could be produced in the reaction medium when using Bi(0Tf)3-4H20 as catalyst. It appeared that these two compounds efficiently catalyze the Mannich-type reaction (Table 7, entries 2 and 3). The reaction does not occur in the presence of 2,6-di-/<7V-buty I-4-methyl-pyridine [DTBMP] (1.0 equiv. of lp, 1.3 equiv. of silyl enol ether, 0.5 mol% of Bi(0Tf)34H20, 1.5 mol% of 2,6-di-/c/V-buty l-4-methy I-pyridine, 22 °C, 20 h, 99% recovery of lp), which indicates that triflic acid is involved in the mechanism (Table 7, entry 4). 

Methyl 4-[( Difluoro-methy 1-silyl)-methoxy]- ElOa, 602 (2OR -> 2F) 1-Methylen-allyl 2,6-E>ifluoro-ElOb,. 585 (OH - OR)... 

A further example of the use of 2//-thiopyrans as surrogates for m-substituted dienes involves the use of the protected 3,4-dihydio-3-(3-oxobutyl)A//-thiopyranA-onc, 3-[2-(2-methyl-l,3-dioxolan-2-yl)ethyl]-4-[tris(l-methy-lethyl)silyl)oxy-2//-thiopyran 328 as an equivalent of l-ethenyl-2-methylcyclohexene in Diels-Alder reactions. The thiopyran reacted with various maleimides to yield the endo cycloadducts and with methyl propenoate to give the exo adduct under either thermal or Lewis-acid-catalyzed conditions. In the latter case concomitant release of the protected ketone functions occurs, acid-catalyzed cyclization of which generates a fused cyclohexenone ring (Scheme 67). Desulfurization, preferably before the aldol cyclization, leads to derivatives of 2,3,4,4a,5,6,7,8-octahy-dro-4a-methylnaphthalenes < 1997CJC681 >. 

Hydroxylamin N,N-Bis-[trifluorme-thyl]-0-(trimethyl-silyl-methy])-E16a, 300 (O-Alkyl.)... 

Furan 2-(tert.-Butyl-dimethyl-silyl)-3-hydroxymethyl-4-methy]- E6a, 117 (H — CH3)... 

Sensitized photooxidation of silyl enolates with singlet oxygen followed by reduction of the hydroperoxides with PPhs in methanol has been used for the preparation of chiral and achiral ketones such as (/f)-6-methyl-2-cyclohexen-l-one starting from R)-2-methy Icy clohexanone. ... 

The Simmons-Smith reaction is the basis of a method for the indirect a methy-lation of a ketone. ° The ketone (illustrated for cyclohexanone) is first converted to an enol ether, an enamine (16-13) or silyl enol ether (12-17) and cyclopropanation via the Simmons-Smith reaction is followed by hydrolysis to give the a methylated ketone. A related procedure using diethylzinc and diiodomethane allows ketones to be chain-extended by one carbon. In another variation, phenols can be ortho-methylated in one laboratory step, by treatment with Et2Zn and... 

A fluoride-induced desilylchlorination of a-chloro-P-silyl ketones has been used to prepare a-methy-lenecyclobutanones and a-methylenecyclopentanones (Scheme 50). ° In this case, the requisite a-chlo-... 

The same group also investigated catalytic cyclization of 2-alkyl-1-ethynylben-zene derivatives carrying silyl ether groups as in 123 and 125 (Scheme 48) [40]. In contrast to Liu s result [44], when silyl ether-substituted 2-methy-l-ethynylbenzene was subjected to the reaction, only silyl ether-substituted indenes 124 and 126 were afforded in good to excellent yields. 

Derivatization. Components with active groups such as hydroxyl, amine, carboxyl, and olefin can be identified by a combination of chemical reactions and GC. For example, the sample can be shaken with bromine water and then chromatographed. Peaks due to olefinic compounds will have disappeared. Similarly, potassium borohydride reacts with carbonyl compounds to form the corresponding alcohols. Comparison of before and after chromatograms will show that one or more peaks have vanished whereas others have appeared somewhere else on the chromatogram. Compounds are often derivatized to make them more volatile or less polar (e.g., by silylation, acetylation, methy-lation) and consequently suitable for analysis by GC. 

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