Trimethylsiloxy

H-pyran synthesis from, 3, 759 bis(trimethylsiloxy) in pyrrole synthesis, 4, 333 chromene synthesis from, 3, 750 cycloaddition reactions with isocyanates, azetidin-2-ones from, 7, 261 dihydropyran synthesis from, 3, 771 fuiyl... 

Methyl 3-trimethylsiloxy-2-butenoate. This reagent silylates primary, secondary, and tertiary alcohols at room temperature without added catalyst. 

A variable pressure oil pump was used in this distillation. Approximately 10 g of a volatile component, consisting mostly of hexamethyl-disiloxane, was obtained at room temperature (15 (in) before the forerun. The forerun contained the desired product and mineral oil from the n-butyllithium solution. The pot residue was about 5 g. The submitters find the disilyl compound thus obtained is contaminated with a trace amount of mineral oil and 4-6% of a vinylsilane, probably 2-methyl-l-trimethylsiloxy-3-trimethylsilyl-2-propene. This impurity becomes quite significant if the reaction medium is less polar than the one described (e.g., too much hexane from n-butyllithium is allowed to remain behind). The spectral properties of the desired product... 

It is generally considered in this notation that methyl groups are attached to silicon atoms. This nomenclature allows structures like trimethylsiloxy-endblocked-polydimethylsiloxane (TMS-eb-PDMS) to be simply represented as MD M (Scheme 2). 

When an organofunctional group replaces a methyl group on a siloxy unit, a superscript is used to describe the unit. The most common groups that are encountered can be symbolized as alkyl (R), hydrogen (H), phenyl (Ph), hydroxyl (OH), trifluoropropyl (F), and vinyl (Vi). Thus, vinyl-endblocked-PDMS is represented by (Scheme 3), and a trimethylsiloxy-... 

As another consequence of the properties of the siloxane bond, the value of n in the common linear trimethylsiloxy-endblocked-PDMS, (M-D -M) can vary from zero to tens of thousands giving a range of viscosity from 0.65 to 2,500,000 centipoise to the polymeric material. This relationship between viscosity and polymer chain length allows PDMS polymers to vary in form from water-like fluids to a flowable gum, while retaining the same chemical character. 

Surprisingly, the size of the silyl protecting group significantly influences the stereochemical outcome of aldol additions performed with the lithium enolates of (S )-l-trimethylsiloxy-and (S)-l-f< rt-butyldimethylsiloxy-l-cyclohexyl-2-butanone. Thus, the former reagent attacks benzaldehyde preferably from the Si-face (9 1), which is the opposite topicity to that found in the addition of the corresponding titanium enolates of either ketone ... 

Stereodivergent aldol addition is also possible when (.S,)-5,5-dimethyl-4-trimethylsiloxy-3-hexanonc (16) is chosen as the enolate precursor. Thus, the lithium enolate generated from 16 by treatment with lithium diisopropylamide and tetramethylethylenediamine leads predomi-... 

Due to their tendency to form (Z)-enolates, ketones usually provide syn-aldols, and anti-se ec-tive chiral ketone enolates are rare. When, however, (S)-5,5-dimethyl-4-trimethylsiloxy-3-hex-anone is deprotonated with (V-(bromomagnesio)-2,2,6,6-tetramethylpiperidine, the (E)-enolate la is assumed to be formed. Subsequent addition to aldehydes delivers anh-aldols 2a and 3a in ratios of between 92 8 and 95 5 and yields of 75-85%53b. 

In the Mukaiyama variation of the aldol reaction, 3-benzoyloxy-2-trimethylsiloxy-l-butene adds to 2-methylpropanal in a stereoselective manner. Best results are obtained in the presence of titanium(IV) chloride, giving the adducts 9/10 in a diastereomeric ratio of 92 8. Hydrolysis of the benzoyl group and subsequent oxidative cleavage of the 1,2-diol moiety liberates / -hy-droxycarboxylic acids593. 

The thermal instability of 37 reduces its applicability with poorly reactive dienes such as vinylcyclohexene and its derivatives 38, unless high pressure (HP) is employed. Ultrasound is not only effective in promoting the cycloaddition of 37 with 38, but sometimes also improves the regioselectivity. Some data are illustrated in Table 4.8 and compared with cycloadditions in refluxing benzene and under high pressure. The reactions of 37 with reactive dienes such as cyclopentadiene and l-(trimethylsiloxy)-1,3-butadiene give a good yield of type D adducts under mild conditions, while with less reactive dienes, such as isoprene and butadiene, poor results are obtained. 

Dimethyl-2(l//)-quinoxalinone (64) gave 6,7-dimethyl-2-trimethylsiloxy-quinoxaline (65) (excess MesSiNHSiMea, trace (NH4)2S04, reflux, 20 h crude solid) and thence 6,7-dimethyl-l-(2,3,5-tri-(9-benzoyl-p-D-ribofurano-syl)-2(l//)-quinoxalinone (66) (l-(9-acetyl-2,3,5-tri-(9-benzoyl-p-D-ribofura-nose, BFs EtjO, CH2CI2, 20°C, 3 h 36% overall). ... 

Danshefsky s diene [19] is the 1,3-butadiene with amethoxy group at the 1-position and a trimethylsiloxy group at the 3-position (Scheme 18). This diene and Lewis acids extended the scope of hetereo-Diels-Alder reactions with aldehydes [20], This diene reacts with virtually any aldehyde in the presence of Lewis acids whereas dienes usually react with only selected aldehydes bearing strongly electron accepting a-substituents. There are two (Diels-Alder and Mukaiyama aldol) reaction pathways (Scheme 18) identified for the Lewis acids catalyzed reactions of Danishefsky diene with aldehydes [21, 22]. The two pathways suggest that these reactions occur on the boundary between the delocahzation band (the pericyclic... 

Trimethylsilylketene and acyl isocyanates generate 4-trimethylsiloxy-l,3-oxazin-6-ones 12 in situ, which smoothly react with the enamines of cycloalkanones to give bicyclic 2-pyridones 13 <96TL(37)4977>. The heterocycles 12 also undergo the Diels-Alder reaction with dimethyl acetylenedicarboxylate or methyl propiolate to furnish substituted 2-pyridones <96TL(37)4973>. 

The potential for coordination depends on the oxy substituents.82 Alkoxy substituents are usually chelated, whereas highly hindered silyloxy groups usually do not chelate. Trimethylsiloxy groups are intermediate in chelating ability. The extent of chelation also depends on the Lewis acid. Studies with a-alkoxy and (3-alkoxy aldehydes with lithium enolates found only modest diastereoselectivity.83... 

Several enolates of 4,4-dimethyl-3-(trimethylsiloxy)-2-pentanone have been investigated.106 The lithium enolate reacts through a chelated TS with high 2,2 -anti stereoselectivity, based on the steric differentiation by the f-butyl group. 

Stereospecificity also is exhibited for dienes having stronger electron-releasing groups, such as trimethylsiloxy. 

Examples of Dienes and Dienophiles. The synthetic value of D-A reactions can be enhanced in various ways. In addition to hydrocarbon dienes, substituted dienes can be used to introduce functional groups into the products. One example that illustrates the versatility of such reagents is l-methoxy-3-trimethylsiloxy-l,3-butadiene... 

Tris(trimethylsiloxy)-methoxy hexatriene undergoes with aliphatic imidazolides in the presence of a Lewis acid a 5C -f 1C cyclocondensation reaction leading t° aromatic products 18]... 

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