Lead Acetylide

Lead Acetylide, PbC/probably), mw 231.21-Lt grey powd, stahle toward HaO. Stated to be prepd by adding CaCj to an aq soln... 

Lead Aceto-Perchlorate A29-L Lead Aceto-Sodium Perchlorate A29 L Lead Acetylide A76-R Lead Azide (Lead Diazide) (LA) A545 to A556... 

Lead(ll) oxide Chlorinated rubber, chlorine, ethylene, fluorine, glycerol, metal acetylides, perchloric acid... 

Condensatron between lithium acetylides and dibromodifluoromethane [124] or dichlorofluoromethane [125] leads to fluorohaloacetylenes (equation 107) Sodium alkyl malonates are also alkylated by dihalogenodifluoromethanes [124] (equation 108) These reactions involve difluorocarbene as intermediate (for the mechanism of the Cp2Br2 condensation, see equation 15)... 

The cyclization of o-halogenobenzoic acids with copper acetylides mainly leads to the formation of five-membered lactones (66JOC4071 69JA6464) (Scheme 115). Only in the case of the reaction of o-iodobenzoic with CuC=C—n-C3H7 does the formation of a mixture of y- and 5-lactones occur (Scheme 116). 

Thus, the cross-coupling of different iodo-A -methylpyrazolecarboxylic acids with copper acetylides leads to closure of the six-membered ring. 

Oppenauer oxidation of the enol ether (34) affords the corresponding 17 ketone (37) (the enol ether is stable to the basic oxidation conditions). This ketone affords the corresponding 17a-ethynyl compound on reaction with metal acetylides. Hydrolysis of the enol ether under mild conditions leads directly... 

The much simpler steroid, 253, was fortuitously found to fulfill this role when injected into animals. Its lack of oral activity was overcome by incorporation of the 7a-thioacetate group. Reaction of the ethisterone intermediate, 77b, with a large excess of an organomagnesium halide leads to the corresponding acetylide salt carbonation with CO2 affords the carboxyllic acid, 251. This is then hydrogenated and the hydroxy acid cy-clized to the spirolactone. Oppenauer oxidation followed by treatment with chloranil affords the 4,6-dehydro-3-ketone (254). Conjugate addition of thiolacetic acid completes the synthesis of spironolactone (255), an orally active aldosterone antagonist. ... 

The most convenient method for the preparation of sodium acetylide appears to be by reaction of acetylene with sodium methylsulfinyl carbanion (dimsylsodium). The anion is readily generated by treatment of DMSO with sodium hydride, and the direct introduction of acetylene leads to the reagent. As above, the acetylide may then be employed in the ethynylation reaction. 

Kupfer-asche, /. copper scale, -azetat, n. copper acetate, -azetylen, n. copper acetylide. -bad, n. copper bath, -barre, /. copper bar copper ingot, -belze, /. copper mordant, -blatt, n. copper foil, -blau, n. blue verditer, azurite. -blech, n. sheet copper, copper foil, -blel, n. copper-lead alloy, -bleiglanz, m. Min.) cuproplumbite. -bleivitriol, m. linarite. -blende, /. tennantite. -blute, / copper bloom (capillary cuprite), -braim, n. tils ore (earthy ferruginous cuprite),... 

The effect of ethylmagnesium iodide on ethoxyacetylene leads to a metal acetylide, which detonate when the medium is stirred. 

The first dip given to a fusehead is known as the flashing composition and is of particular importance. Originally copper acetylide was used for this purpose, but it has been superseded by more stable materials. Three common compositions are based on lead picrate, lead mononitroresorcinate and a mixture of charcoal and potassium chlorate respectively. These materials are suspended in a solution of nitrocellulose in amyl acetate and amyl alcohol, known as Zapon. One or more dips, with intermediate drying, give a layer of suitable thickness. 

The carbide is oxidised with incandescence on warming with lead oxide. See Metal acetylides, below... 

The process is initiated by a double Grignard reaction of 4-pentynoic acid 153, first with 3-butenyl magnesium bromide and subsequently magnesium acetylide followed by silylation of the formed ter-tiaiy hydroxyl function. The cobalt induced polycy-clization leads directly to the fenestrane 157 interestingly, the reaction halts at the stage of 156 when employing the unprotected alcohol. 

The reaction sequence outlined in Scheme 20.30 for the preparation of the chlorinated enyne-allenes was successfully adopted for the synthesis of the C44H26 hydrocarbon 251 having a carbon framework represented on the surface of C60 (Scheme 20.50) [83]. Condensation of the monoketal of acenaphthenequinone (243) with the lithium acetylide 101 afforded the propargylic alcohol 244. On exposure to thionyl chloride, 244 underwent a cascade sequence of reactions as described in Scheme 20.30 to furnish the chloride 248. Reduction followed by deprotection produced 250 to allow a repeat of condensation followed by the cascade transformation and reduction leading to 251. 

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