Boranes acetylene derivs

The compounds 93 (R = Me, Et) are extremely sensitive toward oxidation and moisture and were not isolated in a pure state. Their structures were supported by NMR spectroscopy. Treatment of 93 with pyridine also gives rise to pyridine-l-boraadamantane complex 111 and starting acetylene derivative, via 1,1-deorganoboration. Accordingly, the 1-boraadamantane-TMEDA adduct (TMEDA - bis(dimethylamino)ethane) (along with Me3SnC CSnMc() is formed when the tricyclic borane 93a (R=Me) reacts with TMEDA <2003JOM(687)108>. 

S)-(-)-CITRONELLOL from geraniol. An asymmetrically catalyzed Diels-Alder reaction is used to prepare (1 R)-1,3,4-TRIMETHYL-3-C YCLOHEXENE-1 -CARBOXALDEHYDE with an (acyloxy)borane complex derived from L-(+)-tartaric acid as the catalyst. A high-yield procedure for the rearrangement of epoxides to carbonyl compounds catalyzed by METHYLALUMINUM BIS(4-BROMO-2,6-DI-tert-BUTYLPHENOXIDE) is demonstrated with a preparation of DIPHENYL-ACETALDEHYDE from stilbene oxide. A palladium/copper catalyst system is used to prepare (Z)-2-BROMO-5-(TRIMETHYLSILYL)-2-PENTEN-4-YNOIC ACID ETHYL ESTER. The coupling of vinyl and aryl halides with acetylenes is a powerful carbon-carbon bond-forming reaction, particularly valuable for the construction of such enyne systems. 

Sequential treatment of an ethynylalkanol acetate with butyllithium and a trialkyl-borane produces an allenic borane (23), which when protonated with acetic acid forms an allene, while upon treatment with water affords an acetylene derivative, presumably via a cyclic process (Eq. 51) A novel synthesis of homopropargylic... 

Reaction of acetylenic derivatives of the elements of group 14 with triorganoboranes gives products of 1,1-organoboration [eq. (I)].1 At the same time, allylic boranes react with triple bonds by 1,2-addition mechanism through a six-membered transition state [eq. (2)].2 Therefore two different reaction pathways may be expected for interaction of A113B with Si-, Ge- and Sn-containing acetylenes. 

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. ... 

Syntheses with boranes and acetylene derivs. Allyl-type rearrangement a-Alkoxystyrenes from alkoxyacetylenes... 

Borane-dimethyl sulfide ci.f- thylene from acetylene derivs. s. 8,71 suppl. 31... 

Dilithium tetrachlorocuprate is recommended as an additive for cross coupling of Grignard compounds with tosylates even allylic and benzylic acetates give good yields . a-Methylene-ketones, -carboxylic acids and -lactones have been prepared via sulfides and sulfoxides. A convenient and general synthesis of acetylene derivatives from boranes via the reaction of iodine with lithium 1-alkynyltriorganoborates has been published ar-Nitrostyrenes can be easily obtained by a Wittig synthesis with formaldehyde in an aqueous medium . A new synthesis of unsym. ketones by reaction of dialkyldiloroboranes with lithium aldimines has recently been published . Metallo aldimines have also served for the synthesis of a variety of other compound classes such as a-hydroxyketones, a-keto acids, nitriles, and for the asym. synthesis of a-amino acids . Polycondensations of malononitriles with benzylic chlorides have been carried out quantitatively under mild conditions in dimethyl sulfoxide with triethylamine as acid acceptor . Carbonyl compounds can react with dibromoacetonitrile to yield a-bromo esters with additional carbon atom . ... 

Cyanogen bromide borane Synthesis of tran -ethylene derivs. from acetylene derivs. 

Syntheses via lithium 1-alkynyltriorganoborates Acetylene derivs. from boranes... 

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)... 

Methanesulfinyl chloride n-butyHithium Acetylene derivs. from boranes s. 28, 864 suppl. 29... 

Bis-(3-methyl-2-butyl)borane cis- and frans-a, -Ethylenehalides from acetylene derivatives... 

Hydrozirconations of both vinyl and acetylenic boranes by Srebnik et al. led to 1,1-dime-tallo reagents, which offer the benefits as coupling partners of alkyl- and vinylboranes, respectively [59—62], Initial trials were conducted with B-alkenylborabicyclo[3.3.1]nonanes, but these led to unstable dimetallics. Replacement of the 9-BBN fragment with the pina-colborane-derived analogue produced stable dioxaborolanes 61 (Scheme 4.34). 

CARBORANE. A cry stalline compound composed of boron, carbon, and hydrogen. It can be synthesized in various ways, chiefly by the reaction of a borane (penta-or deca-) with acetylene, either at high temperature in the gas phase or in the presence of a Lewis base. Alkylated derivatives have been prepared. Carborancs have different structural and chemical characteristics and should not be conTused with hydrocarbon derivatives or boron hydrides. The predominant structures arc the cage type, the nest type, and the web type, these terms being descriptive of the arrangement of atoms in the crystals. Active research on cargorane chemistry has been conducted under sponsorship of the U.S. Office of Naval Research, http //www.onr.navy.mil/... 

See also acetylenic compounds, alkylmetals, alkynes, azides, boranes, CYANO COMPOUNDS, DIENES, HALOACETYLENE DERIVATIVES, HALOGEN OXIDES, METAL ACETYLIDES, METAL EULMINATES, OXIDES OF NITROGEN... 

This complex chiral hydride 12 reduces acetylenic ketones such as 13 with reasonable selectivity.1 The other enantiomer of 14 comes from reduction of 13 with the enantiomeric reagent derived from NOVRAD. Note that the absolute sense of the induction in the reduction of 13 is the same with 12 and with the Alpine borane from (+)-a-pinene, below. 

An early success4 was Midland s Alpine-Borane , derived from 9-BBN 28 and a-pinene 22. Hydroboration takes place from the less hindered side of the double bond, away from the gem dimethyl groups, to give alpine borane 29. The reagent works well for acetylenic alcohols and the transition state 30 puts the acetylene in the outside position. 

Some methyl acetylenic ketones are reduced with slightly less efficiency, but this can be improved by using NB-Enantrane11 or an analogous Alpine-Borane derivative with a substituent on the... 

General Synthesis.—Terminal acetylenes can be transformed into carboxylic acids by conversion into the trimethylsilyl derivatives followed by addition of a dialkyl-borane and oxidative hydrolysis (Scheme 1). Conjugated enynes can undergo a similar conversion, and yields throughout are high. 

Midland and coworkers [13,14] achieved the reduction of sterically less congested propargyl ketones with AIpine-Borane. The reduction is accomplished using 2 equiv of 0.5-M solutions of AIpine-Borane (Table 26.11) [14]. Terminal acetylenic ketones and acetylenic ketoesters are completely reduced after 8 h at room temperature. Internal acetylenic ketones require 1-4 days at room temperature for complete reductions. The optically active chromanyl substrates (entries 7, 8) yield diastereomeric alcohols with (R,R) R,S) ratios of 85 15 for internal and 91 9 for the terminal acetylenes with the AIpine-Borane derived from (-i-)-a-pinene of 100% ee. The reagent obtained from pure (-)-a-pinene affords 18 82 ratio of the two diastereomeric internal propargylic alcohols. 

Two novel routes to triethylborane have been reported. Irradiation of bromoethane and aluminium powder with ultrasound gives ethyl aluminium sesquibromide which on treatment with triethoxyborane gives triethylborane in good yields and a laser initiated gas phase reaction between diborane and ethene gives yields of upto 91%. Allylic boranes have been prepared from allylpotassiiim derivatives and chloroboranes. Hydrolysis leads to the Isomerised olefin and the technique has been used to transform (+)-a-pinene into (+)-3-pinene. Condensation reactions between allylboranes and acetylenes have been developed into a convenient method for the synthesis of bicyclo[3.3.l]nonane derivatives. Mainly linear alkyl derivatives of 9-BBN have been synthesised from the, reaction of iron carbonyls and the organoborane in a Fischer-Tropsch type reaction. ... 

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