Acetylene as precursor

The related lithium(phenylthio)cyclopropylcuprate, prepared from cyclopropyllithium and PhSCu, has been extensively used in the synthesis of /1-cyclopropyl enones by coupling with the corresponding fl-iodo enones (equation 10)34 36. Repetitive regioselective coupling of ethynylcyclopropane units by this method led to polyspirocyclopropyl acetylenes as precursors to [NJpericyclynes37. 

For the corrosive line, the reactor is fully teflon-coated so we can use veiy aggressive products such as chlorides, ammonia or acetylene as precursors. It is possible to use silicon chloride or titanium chloride as precursor products to produce nanopowders containing silicon or titanium. An internal and an external scrubber neutralise the chloride with water (internal scrubber) and sodium hydroxide (NaOH). If we start with liquids or gases for precursors, the particle sizK distribution of the end product will be much better controlled. 

Poly(carborane—siloxane—acetylene) as Precursor to High-Temperature Thermoset and Ceramic... 

Acetylenic compounds have often been used as precursors to certain pyrroles. Thus, 2-butyne-l,4-diol reacts with aniline ia the presence of alumina to produce A/-phenylpyrrole [635-90-5] (27). 

The electronic properties of germanium have led to an interest in incorporating the element into extended polymeric chains due to the intrinsic properties of the polymers themselves or in their use as precursors for material synth-esis. Catalytic co-polymerization of the germylene Ge[N(SiMe3)2]2 with various substituted acetylenes leads to... 

Ethynylated dihydrofullerenes serve as precursors for buckydumbbells (Scheme 3.3). Coupling of the desilylated compound 10 with CuCl leads to the dimer 11 [24]. Reaction of Cjq with the acetylide Li-C=C-Li leads to the dimer with a bridge consisting of one acetylene unit only. Electronic interaction between the fullerene-units in these two buckydumbbells is negligible. Further examples of CgQ-acetylene-hybrids synthesized by using cyclopropanation reactions are shown in Chapter 4. 

Aryl acetylenic derivatives continue to exhibit interest as precursors for fused ring systems. Foe example, treatment of l-methyl-5-(trimethylsilylethynyl)uracil with ammonium fluoride leads to 3-methylfuro[2,3- 1pyrimidin-2(3//)-one in good yield <2006JMC391>. 

These are good dienophiles. and aryl vinyl sulfones have found use as equivalents of ethylene and ketene through functional modifications of their adducts. However, as the base-induced elimination of a sulfinic acid to yield an olefin occurs only with difficulty, they are not direct precursors of acetylene equivalents, unless suitably modified as in ( )-l-phenyl-sulfonyl-2-trimethylsilyl ethylene (PhS02-CH=CH-TMS). In its cycloadducts the elimination to an alkene is smoothly realized by the fluoride ion. If an alkylation step is previously carried out on the adduct, the overall process realizes an indirect addition of a terminal acetylene, as in the examples given here [533]. 

Consequently, CVD is now the method-of-choice for the synthesis of CNTs. As discussed in Chapter 4, these methods consist of the decomposition (typically thermal) of a hydrocarbon precursor on the surface of catalytic metal nanostructures. Methane and acetylene have been used most extensively as precursors other alternatives now include CO, C2H4, and methanol/ethanol. As with any CVD approach, this method is easily scaleable, and is used to generate kilogram quantities of CNTs for an ever-increasing laundry list of applications. 

With this restriction in mind, other solutions of the same central idea and without the participation of free radical species are conceivable. For instance. 1,4 elimination of acetic acid shown in route H would yield ketene V directly, a contention that finds support in the favorable 1,5 elimination portrayed in XII (see Scheme 54.5). Analogously, a benzylic carbene precursor would also be in a position to give an acetylene if route F of Scheme 54.3 is handled in such a way as to prevent charge development. In fact, carbene XIV that would result from the 1,1 elimination of acetic acid from I, has been shown to give aldehyde III when furyl-phenyl diazomethane (XV) (an efficient carbene generator) was used as precursor. ... 

By contrast, acetylenic chemistry has been developed by Hofmann La Roche based on the use of propanone, diketene and acetylene as a pathway to linalol from the precursors methylheptenone and dehydrolinalol which itself has in turn been utilised for the synthesis of the (Cl3) ionones and subsequently in related methodology for the C15 alcohol, nerolidol all of which are referred to again subsequently. 

The stability of the -C -Si< bond has been known for a long time But on the other hand they are reactive compounds which undergo either - as precursors to vinylsilanes - various types of addition reactions or - as only silyl-protected acetylenes - an electrophilic substitution under Friedel-Crafts conditions in presence of catalytic amounts of Lewis acids The — SiR3 moiety has a highly useful protecting and/or activating function. 

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