Boranes with acetylides

Ignition or explosive reaction with metals (e.g., aluminum, antimony powder, bismuth powder, brass, calcium powder, copper, germanium, iron, manganese, potassium, tin, vanadium powder). Reaction with some metals requires moist CI2 or heat. Ignites with diethyl zinc (on contact), polyisobutylene (at 130°), metal acetylides, metal carbides, metal hydrides (e.g., potassium hydride, sodium hydride, copper hydride), metal phosphides (e.g., copper(II) phosphide), methane + oxygen, hydrazine, hydroxylamine, calcium nitride, nonmetals (e.g., boron, active carbon, silicon, phosphoms), nonmetal hydrides (e.g., arsine, phosphine, silane), steel (above 200° or as low as 50° when impurities are present), sulfides (e.g., arsenic disulfide, boron trisulfide, mercuric sulfide), trialkyl boranes. 

NITRATE de ZINC (French) (7779-88-6) Noncombustible, but will enhance the combustibility of other materials. Many chemical reactions can cause fire and explosions. A strong oxidizer. Violent reaction with reducing agents, strong oxidizers, combustible materials, organic substances, metallic powders, acetic anhydride, tert-butylhydroperoxide, carbon, dimethylformamide, metal cyanides, metal sulfides, phosphorus, sodium acetylide, sulfur, thiocyanates. Incompatible with amines, ammonium hexacyanoferrate(II), boranes, cyanides, citric acid, esters, hydrazinium perchlorate, isopropyl chlorocarbonate, nitrosyl perchlorate, organic azides, organic bases, sodium thiosulfate, sulfamic acid. Attacks metals in the presence of moisture. 

Related techniques have been developed to prepare (Z-,Z)- (Z-, )- and ( -, )- dienes. Hydroboration of diacetylenes followed by protonolysis is a convenient route to (Z-,Z)-dienes, as in the conversion of 89 to 90. The requisite symmetrical diacetylenes are prepared by oxidative coupling with oxygen and cuprous chloride, as in the conversion of 1-cyclohexylethyne (78) to 89. Unsymmetrical conjugated dienes can be prepared by formation of a diacetylene ate complex, prepared from disiamylmethoxyborane by sequential reaction with different acetylides. A similar borane route to unsymmetrical diacetylenes uses dicyclohexyl methyl-thioborane. ... 

In another copper-catalyzed reaction, cross-coupling of alkynes with phosphi-ne-boranes was followed by surprising oxidation to yield ketones (Scheme 69) [122]. The active species was proposed to be a copper phosphido-borane complex, formed by proton transfer to a Cu-OH group. Formation of a Cu-acetylide followed by P-C reductive elimination would then yield a phosphino-alkyne, whose subsequent Cu-mediated air oxidation yields the ketone. 

A soln. of 3,3-dimethyl-1-butyne in ether at —78° under Nj treated slowly with n-butyllithium, the formed Li-acetylide added slowly via cannula to triisopropoxy-borane in the same solvent with stirring, kept at —78° for 2 h, treated with anhydrous HCl, and allowed to warm to room temp. 3,3-dimethyl-1-butynyldiisopropoxy-borane. Y 90%. Attempted transesterification of the products resulted in B-C bond cleavage. F.e.s. H.C. Brown et al., Tetrahedron Letters 29, 2631 (1988). 

Triacetylenic boranes are derived from lithium acetylides and boron trifluoride etherate in THF at —20 °C. They react with ethyl diazoacetate to give homologated propargyl esters (7) after hydrolysis. Hydration of these iSy-acetylenic esters using mercuric ion is regiospecific only y-keto-esters (8)... 

Cyclohexene added under Ng to a soln. of borane in tetrahydrofuran, stirred overnight at room temp, (or 3 hrs. at 50 ), treated with lithium acetylide-etliylene-... 

There have been significant discoveries of methods that enable the enantioselective addition of an alkyne to an aldehyde or a ketone [182]. The resulting chiral propargyl alcohols are amenable to a wide variety of subsequent structural modifications and function as useful, versatile chemical building blocks. In 1994, Corey reported the enantioselective addition reactions of boryl acetylides such as 292, prepared from the corresponding stannyl acetylenes (e.g., 291) in the presence of the oxazaborolidine 293 as the chiral catalyst (Scheme 2.36) [183]. Both aliphatic and aromatic aldehydes were demonstrated to participate in these addition reactions, which proceeded in high yields and with impressive enantioselectivity. The proposed transition state model 295 is believed to involve dual activation both of the nucleophile (acetylide) and of the electrophile (aldehyde). The model bears a resemblance to the constructs previously proposed for alkylzinc addition reactions (Noyori, 153) and borane reductions (Corey. 188). 

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