Trialkylsilyl precursors

An important direction in the development of heterogeneous catalysts grafted onto mesoporous silicas is exploiting the rich chemistry of metal cluster catalysts bearing carbonyl or alkylphosphine ligands or both is exploiting a broad library of trialkylsilyl precursors with cluster functions, developed in particular by Bronstein et al. [28]. 

Nitro compounds have been converted into various cyclic compounds via cycloaddidon reactions. In particular, nitroalkenes have proved to be nsefid in Diels-Alder reactions. Under thermal conditions, they behave as electron-deficient alkenes ind react v/ith dienes to yield 3-nitrocy-clohexenes. Nitroalkenes c in also act as heterodienes ind react v/ith olefins in the presence of Lewis acids to yield cyclic alkyl nkronates, which undergo [3- 2 cycloaddidon. Nitro compounds are precursors for nitnie oxides, alkyl nitronates, and trialkylsilyl nitronates, which undergo [3- 2 cycloaddldon reacdons. Thus, nitro compounds play important roles in the chemistry of cycloaddidon reacdons. In this chapter, recent developments of cycloaddinon chemistry of nitro compotmds and their derivadves are summarized. 

Brus and co-workers produced nanoparticles of CdSe from the pyrolysis of the single-molecular cadmium selenate precursor [Cd(SePh)2].392 The similar metal(benzylthiolate) compounds [M(SCH2C6i Is)2] (M = Zn, Cd) were also used in the solid-state preparation of ZnS and CdS particles and produced mixtures of the hexagonal and cubic phases of the crystallites, with sizes of 5nm, on thermolysis between 200 °C and 400 °C under nitrogen.393 The bis(trialkylsilyl)chalco-genides [(Me3SiE)2Cd] (E = S, Se), prepared by heterocumulene metathesis as in Equation (11), were used to produce nanoparticles. If the reactions are carried out in TOPO, TOPO-passivated CdE nanoparticles can be obtained although there was little control over particle size 394... 

Following the work of Mclnnes,289,290 methanolysis in the presence of potassium carbonate was used to prepare methyl 6-O-acetyl- and methyl 6-0-octadecanoyl-/3-D-glucopyranoside,291 o-nitrophenyl /3-D-galactopyranoside 6-phosphate,292 methyl 5-thio-a-D-glucopyranoside 6-phosphate,293 and 6,6 -di-0-hexadecanoyl-a,a-trehalose,294 from the appropriate, per-0-(trialkylsilyl)ated precursors. 

Trialkylsilyl enol ethers of acyl silanes have been prepared using a variety of routes and can be excellent precursors to acyl silanes through simple hydrolysis. 

Enol silyl ether is one of the most useful organosilicon reagents, and various methods for the preparation from a variety of precursors have been investigated. The most widely used method is silation of enols or enolates of ketones or aldehydes with trialkylchlorosilanes. The reaction of ketones with triethylamine and chlorotrimethyl-silane in DMF alTords the thermodynamic equilibrium mixtures of enol silyl ethers (eq (48)) [44]. The use of silyl trifiates instead of chlorosilanes generally shortens the reaction time and permits the preparation of some enol silyl ethers which are difficult with halosilanes (eq (49)) [45]. Trialkylsilyl trifiates are also employed for the syntheses of enol silyl ethers of esters and S-alkyl thiol esters (eq (50)) [46]. 

The most recent successful method for generating 3-pyridynes uses 4-trialkylsilyl-3-pyridyl triflates as precursors (a similar approach but with a bromine in place of the triflate group is considerably less successful). They were synthesized by o-metallation... 

Scheme 22.14 A new approach for parent polyphenylenes by "shaving hairy precursor polymers (a) and a concrete chemistry applied to a trialkylsilylated SPC polymer (b).

Investigations of phthalimide photochemistry in the authors laboratories have concentrated on SET-induced excited-state reactions with a-trialkylsilyl substituted ethers, thioethers, and amines. These efforts have uncovered several interesting photochemical reactions. For example, in an early effort simple, a-silyl-substituted ethers, thioethers, and amines were observed to undergo efficient photoaddition reactions with phthalimide and its N-methyl derivative (Scheme 5.4) [20]. In these processes, thermodynamically/kinetically driven SET from the a-silyl donors 13 to excited phthalimide leads to formation of ion radical pairs 16 (Scheme 5.5). Solvent (MeOH) promoted desilylation of the cation radicals 16 and protonation of the phthalimide anion radicals 15 then provides radical pairs 17, the direct precursor of adduct 14. 

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