Acetylene, alkylation

Die partielle Reduktion von Alkinen zu Alkenen durch Chrom(ll)-L6sungen in ammoniakalischer Ammoniumchlorid- Oder salzsaurer Losung ist nur teilweise moglich. Wahrend Acetylen, Alkyl- und Aryl-al-kine Alkene bildcn, wcrden Dialkyl-alkine nicht angegriffen (s. Bd. V/lb, S. 584). Die durch Reduktion mit Chrom(II)-sulfat entstehenden Alkene besitzen uberwicgend(ran.v-Konfiguration (80-90% d.Th. s. Bd. V/lb, S. 783, vgl. auch 584). 

The reactivity of dichloro carbene towards acetylenic bonds was systematically investigated by Dehmlow19, 20 with respect to substitution of the acetylene, especially those containing additional C-C multiple bonds. It was shown that with aiyl alkyl acetylenes, e.g. 1-phenyl-butyne-l, often the normal cyclopropenone formation occurs only to a minor extent (to yield, e.g. 14), whilst the main reaction consists of an insertion of a second carbene moiety into the original acetylene-alkyl bond (giving, e.g. 15) ... 

Reduction of acetylenes. Alkyl phenylacetylenes are reduced by chromium(II) perchlorate-triethylamine to cw-olefins in high yield. Terminal acetylenes are also reduced readily, but dialkylacetylenes are not reduced. 

Organomagnesium compounds, acetylenic, alkylation, SO carbonation, 425 coupling with CICN, 82... 

Polymeric precursors have been developed which are stable at room temperature and when polymerized convert to ceramics in high yield. Such precursors may be synthesized by reaction of a vinylsilane, vinylmethylsilane, acetylene silane, or acetylene alkyl silane with a borane or a borane amine derivative The reactants are mixed in an inert atmosphere, either neat or in an aprotic solvent like acetonitrile, tetrahydrofuran, or a hydrocarbon, or in a mixture of such solvents. The reaction mixture is heated for 0.1 to 120 h at 90-170°C. The solvent, if any, is then removed. The polymer is pyrolyzed in argon or N2 at SOO-ISOO C for 1 h. BN and other ceramics such as B4C, or SipB QNs compounds can be made, where p, q, r, and s have various numerical values. To date, no measurements of the crystallographic form of the resultant BN compound have been made. Other precursors convertible to BN include poly (2-vinylpentaborane) oligomers. ... 

The construction span is usually the functional span shown in Table 1 but not always since the construction span must include the constructed link and hence at least the a-carbon on both sides even though in some cases there is no product functionality on one synthon (/ = 0 in product, as in alkylation), e.g., acetylene alkylation (Table 1). 

USE In the manuf of pharmaceutical hydrochlorides, vinyl chloride from acetylene, alkyl chlorides from olefins, and arsenious chloride from arsenious oxide. In the chlorination of rubber, as a gaseous flux for babbitting operations. In Organic reactions involving isomerization, polymerization, and alkylation. For making chlorine where economical. 

Single-electron Transfer Carbene Mechanisms. The vast majority of reactions of LDA owe their mechanism to the basic character of the reagent some recent experiments have shown that LDA may behave very differently in the presence of alkyl halides and dihalides (specifically iodides), 7r-deficient aromatic heterocyclic compounds (Scheme 8, eq 7), a-bromo imines, conjugated acetylenes, alkyl sulfonates, or benzophenone. In these instances, it has been shown that LDA may act as a single-electron transfer donor as in the case of anthracene and perylene, or via carbene mechanism in the case of benzyl halides. Some substrates exhibit competition between multiple mechanisms (Scheme 8, eq 8, ref 160). 

Cycloadditions. The dienophilic properties of ( )-phenyl-sulfonyl-2-trimethylsilylethylene allow the preparation of adducts with reactive dienes such as cyclopentadiene and anthracene. The adducts are smoothly converted to alkenes upon treatment with fluoride ion, establishing the equivalence of the title reagent to acetylene. Alkylation of the a-sulfonyl carbanion can precede the elimination such that synthetic equivalents to HC CH, HC CD, and RC CH are available. The use of this reagent is highlighted by the synthesis of several functionalized dibenzobarrelenes (eq 1). The equivalency to DC CD and RC=CD is illustrated by the preparation of deuterated derivatives. 

Both strategies are applied to the preparation of alkynes. In this section we shall see how to prepare alkynes by carbon-carbon bond-forming reactions. By attaching alkyl groups to acetylene (alkylation), more complex alkynes can be prepared. 

Fragmentation of vinylic and acetylenic alkyl ethers Dominant homolysis of the alkyl C-C bond next to the O atom on the saturated side, leading to C3H50 (m/z 57) for vinylic and C3H30 (m/z 55) for acetylenic ethers of primary aliphatic alcohols. For alkyl (C 5) vinyl ethers, ethanol elimination after triple H transfer. [M-15]+ in vinyl ethers predominantly by elimination of the vinyl CH2 after H rearrangement. 

Acetylenes, alkyl or aryl, polymers with Ag(l) or Cu(I), 142 4-Acetyl-4-(ethoxycarbonyl) -1,6-heptadiene, polymers of, 83 Acetylferrocene, see also Diacetylferrocene polymers of, 9, 16,24 4-Acetyl-1,6-heptadiene, polymers of, 81 Acrylamide, copolymers with 2,6-dicyano-1,6-heptadiene, 80 Acrylic acid, copolymers with 4,4-di(ethoxycarbonyl)-l,6-heptadiene, 84 Acrylonitrile... 

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