One-pot conversion of carboxylic acids to aldehydes through treatment of acyloxy-9-borabicyclo[3.3.1]nonanes with lithium 9-boratabicyclo[3.3.1]nonane

Carboxylic acids are readily reduced to the corresponding aldehydes in high yields by treatment of acyloxy-9-borabicyclo[3.3.1]nonanes with lithium 9-boratabicyclo[3.3.1]nonane (Li 9-BBNH) at room temperature.     

B-bromo-9-borabicyclo[3.3.1]nonane. A convenient and selective reagent for ether cleavage

In methylene chloride solution, B-bromo-9-borabicyclo[3.3.1]nonane (BBr-9-BBN) readily cleaves, in excellent yield, a variety of ethers of representative structural types. The reagent can also be used for selective cleavage of one of the ether groups in a molecule containing more than one such group.     

Facile and convenient synthesis of B-amino-9-borabicyclo[3.3.1]nonanes. Aminoboration of lsocyanates

The reaction of 9-borabicyclo[3.3.1]nonane (9-BBN) with aliphatic and aromatic primary and secondary amines in tetrahydrofuran (THF) at 65°C proceeds rapidly and quantitatively with evolution of hydrogen and the formation of the corresponding B-amino-9-borabicyclo[3.3.1] nonane (B-amino-9-BBN). Simple evaporation of THF from the reaction mixture gives the B-amino-9-BBN derivatives in high yield and purity. These B-amino-9-BBN derivatives are reactive towards alkyl and aryl isocyanates. Consequently, the aminoboration of various isocyanates has been studied using B-phenylamino-9-BBN. Thus, two equivalents of isocyanates react with one equivalent of B-phenylamino-9-BBN to afford, following the hydrolysis of the intermediate with ethanolamine, N, N'-disubstituted-N -(phenylamido)-ureas in excellent yields. A plausible mechanism for this aminoboration reaction of isocyanates is also presented.     

Organoboration of alkynlystannanes: XIX. Stannacyclopentadienes via organoboration of diethylnyldimethylstannane with B-alkyl-9-borabicyclo[3.3.1]nonanes

Tricyclic heterocycles (8) containing a stannacyclopentadiene unit are obtained as the major products (ρ 80%) from the reaction between diethynyldimethylstannane and B-alkyl-9-borabicyclo[3.3.1]nonanes (2). By comparison with the analogous reaction of ethynyltrimethylstannane (1) it is shown that compounds 8 are the kinetically controlled products. Assignments of the structure of 8 and those of some minor products are based on multinuclear NMR spectra (¹H, ¹¹B, ¹³C, ¹¹⁹Sn NMR).     

Generation of chiral boron enolates by rhodium-catalyzed asymmetric 1,4-addition of 9-aryl-9-borabicyclo[3.3.1]nonanes (B-Ar-9BBN) to alpha,beta-unsaturated ketones

Asymmetric 1,4-addition of 9-phenyl-9-borabicyclo[3.3.1]nonane (2m) to 2-cyclohexenone (1a) proceeded with high enantioselectivity in toluene at 80 degrees C in the presence of 3 mol % of a rhodium catalyst generated from [Rh(OMe)(cod)]2 and (S)-binap to give a high yield of boron enolate (S)-3am, which is 98% enantiomerically pure. Reaction of the boron enolate 3am with electrophiles, methanol-d, propanal, and allyl bromide, gave the corresponding 2-substituted (3S)-3-phenylcyclohexanones with perfect regio- and diastereoselectivity.     

The hydroboration of 3-butenyl derivatives with 9-borabicyclo[3.3.1]nonane

The hydroboration of 3-butenyl derivatives, CH₂CHCH₂CH₂X where X represents OH, OMe, OAc, Cl, as well as the related carboxylic ester, CH₂CHCH₂COOEt, and the nitrile CH₂CHCH₂CN, with 9-borabicyclo[3.3.1]nonane (9-BBN) proceeds with remarkably high regio-selectivity. The boron is placed essentially on the terminal carbon (?98%), yielding stable organoboranes which can be readily oxidized to alcohols or subjected to other reactions. The yields of alcohols in the hydroboration-oxidation procedure are satisfactory, in the range of 82–99%. The hydroxy group liberates hydrogen rapidly and quantitatively but no further reaction is observed and hydroboration of the carboncarbon double bond then proceeds normally. The chloro and methoxy groups are not affected by 9-BBN, whereas, the ester and nitrile groups are slightly (1.5–4.0%) reduced by the reagent at 25°C. Even this small amount of reduction can be circumvented or minimized by carrying out the hydroboration at 0°C. Although this procedure requires somewhat longer reaction times, the products are cleaner and the yields are higher.     

Oxymercuration. Substituted 9-oxabicyclo[4.2.1]- and 9- oxabicyclo[3.3.1]nonanes

Oxymercuration of cis, cis-1, 5-cyclooctadiene ( 1 ), followed by treatment with potassium iodide and subsequent reaction with iodine, leads to six isomeric diiodides which represent the three possible stereoisomers 2 , 3 , and 4 of 2, 5-diiodo-9-oxabicyclo[4.2.1]nonane as well as 5 , 6 , and 7 of 2, 6-diiodo-9-oxabicyclo[3.3.1]nonane. The isolation, structure determination and some reactions of these diiodo compounds 2 – 7 are described.     

3,7-disubstituted bicyclo [3.3.1] nonanes—II : Synthesis and conformation of some 3,7-disubstituted 9-oxobicyclo [3.3.1] nonanes

Condensation of pyrrolidine enamines of 4-alkylcyclohexanones with methyl α-(bromomethyl)acrylate affords methyl 7β- and 7α-alkyl-9-oxobicyclo [3.3.1] nonane-3α-carboxylates in a ratio of 3:2. The mechanism of the annelation reaction is discussed. The conformations of the reaction products and their epimers have been studied by means of PMR spectroscopy.     

Organoboron compounds: CDIV. A hydride transfer reacton in the series of ate complexes of 7-substituted 3-alkyl-3-borabicyclo[3.3.1]nonanes and 3-alkyl-3-borabicyclo[3.3.1]non-6-enes

The ate complexes of 7-substituted 3-alkyl-3-borabicyclo[3.3.1]nonanes and of 3-alkyl-3-borabicyclo[3.3.1]non-6-enes react with acetyl chloride under mild conditions by an intermolecular β-hydride transfer mechanism to form 5-substituted 3-methylenecyclohex-1-ylmethyl(dialkyl)boranes. The latter compounds were converted, by oxidation with alkaline hydrogen peroxide, to 3-substituted 1-methylene-5-hydroxymethylcyclohexanes. The reaction of cycloalkylmethyl(dialkyl)boranes with aromatic aldehydes was applied to the synthesis of 1,3-di- and 1,3,5-tri-methylene derivatives of the cyclohexane series.     

Olefin-alkyl group exchange of B-alkyl-9-borabicyclo-[3.3.1]nonanes. Evidence for a dehydroboration-hydroboration process

B-Alkyl-9-borabicyclo[3.3.1]nonanes (9-BBN) undergo a rather facile olefin-alkyl group exchange process when refluxed with an olefin in tetrahydrofuran. Kinetic and competition studies support a dehydroboration-hydroboration process.     

Conformational behavior of 3-borabicyclo[3.3.1]nonanes: 1. Study of molecular dynamics in 3-methoxy-7α-phenyl-1,5-dimethyl-3-borabicyclo[3.3.1]nonane

3-Methoxy-7α-phenyl-1,5-dimethyl-3-borabicyclo[3.3.1]nonane 5 in solution at room temperature exists in the double chair conformation, as shown by NMR studies. Increasing the temperature leads to an increase in the population of the chair–boat conformation. At decreased temperature hindered rotation around the B---O bond is observed for 5. Dissolving 5 in deuteropyridine leads to the reversible formation of complex 6, which exists in the chair–boat conformation. The chair–boat conformation is also the most stable one for chelate compound 7 with a tetracoordinated boron atom.     

Preparation of 2,9-dioxabicyclo[3.3.1]nonanes. A model for tirandamycin

An efficient synthesis of a 2,9-dioxabicyclo[3.3.1]nonane system, similar to that of tirandamycin, is accomplished from 2,3-dimethylfuran.     

A new method for the synthesis of 3,7-diazabicyclo[3.3.1]nonanes

Russian Chemical Bulletin -     

Selective reduction of tertiary alkyl,benzyl, and allyl halides to hydrocarbons using lithium 9,9-di-n-butyl-9-borabicyclo[3.3.1]nonanate

The title 9-borabicyclo[3.3.1]nonane(9-BBN) ate complex (1) brings about selective removal of tertiary alkyl, benzyl and allyl halides to give the corresponding hydrocarbons in excellent yields without concomitant attack on secondary, primary and aryl derivatives. The reduction of cis- and trans - 4 - t - butyl - 1 - methylcyclohexyl chlorides (2) with 1 gives 4 - t - butyl - 1 - methylcyclohexanes (3) with partial inversion of configuration in cyclohexane, while that in benzene gives thermodynamically stable trans-3 predominantly. The reactions of 1,1 - dimethyl - 5 - hexenyl chloride (4) and 1,7,7 - trimethylbicyclo[2.2.1]hept - 2 - yl chloride (8) with 1 proceed with the rearrangements characteristic to a carbonium ion intermediate. The reduction of 1 - ethyl - 1 - methylpentyl chloride with 1 follows a second-order rate equation.     

A facile method for the stereoselective Horner-Wadsworth-Emmons reaction of aryl alkyl ketones

Excellent Z or E selectivity was observed in the Horner-Wadsworth-Emmons (HWE) reactions of methyl bis(2,2,2-trifluoroethyl)phosphonoacetate or ethyl 2-fluoro-2-diethylphosphonoacetate with aryl alkyl ketones bearing substituents on an aromatic moiety employing Sn(OSO2CF3)2 in the presence of N-ethylpiperidine.     

Cationic-lanthanide-complex-catalyzed reaction of 2-hydroxychalcones with naphthols: Facile synthesis of 2,8-dioxabicyclo[3.3.1]nonanes

Cationic lanthanide complexes [Ln(CH₃CN)₉]³⁺[(AlCl₄)₃]^3–·CH₃CN served as efficient catalysts for the tandem Friedel–Crafts alkylation/ketalization reaction of 2-hydroxychalcones with naphthols/substituted phenols to produce diaryl-fused 2,8-dioxabicyclo[3.3.1]nonanes in moderate to high yields. The high catalytic efficiency of the cationic lanthanide complex [Yb(CH₃CN)₉]³⁺[(AlCl₄)₃]^3–·CH₃CN compared with that of YbCl₃ can be attributed to the increased Lewis acidity of the Yb species as a result of cation formation.