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.     

Palladium-catalyzed cross-coupling of B-benzyl-9-borabicyclo[3.3.1]nonane to furnish methylene-linked biaryls

[reaction: see text] Benzylboranes are noticeably uncommon partners within Suzuki-Miyaura coupling reactions. B-Benzyl-9-BBN was successfully coupled to a range of aryl/heteroaryl bromides, chlorides, and triflates to give pharmacologically important methylene-linked biaryl structures. Activated, deactivated, and sterically hindered substrates were successfully coupled in high yield using Pd(PPh(3))(4) or Pd(OAc)(2) with SPhos as the catalyst system.     

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.     

Novel synthesis of tertiary alkyl,secondary and tertiary benzyl,and allyl selenides from the corresponding alcohols

We report an efficient synthesis of the title compounds from alcohols and selenols. The scope and limitations of the new method are disclosed.     

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.     

Two-Dimensional Chromatographic Analysis of Polystyrene-block-poly(methyl methacrylate) Copolymers Synthesized by Selective Oxidation of Polystrene-9-borabicyclo[3.3.1]nonane

Summary: The preparation of polystyrene block methyl methacrylate copolymers (PS-b-PMMA) is described. The polystyrene segment was prepared by anionic polymerization and the methylmethacrylate segment was prepared via free radical autoxidation of a borane agent attached to the styrene chain. 1 The chemistry involves a transformation of the anionic polymerization process to borane chemistry by firstly producing polystyrene with chain end unsaturated alkyl functional groups prepared using a n-butyllithium initiator and termination with allylchlorodimethylsilane. Secondly, the unsaturated macroinitiator end was hydroborated by 9-borabicyclo[3.3.1]nonane (9-BBN) to produce a borane terminated PS. Thirdly, the borane group at the chain end was selectively oxidized and converted to polymeric radicals in the presence of methyl methacrylate which then initiated radical polymerization to produce block copolymers. The polymer obtained was characterized using several chromatographic techniques including LC-CC (liquid chromatography under critical conditions) for the polystyrene segments and two-dimensional chromatography with LC-CC in the first dimension and SEC in the second. The results show that block formation was successful although significant homopolymerization of methyl methacrylate is also obtained.     

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.     

Molecular structure of 3,7-dimethyl-9-thia-3,7-diazabicyclo[3.3.1]nonane-9,9-dioxide

By a single crystal X-ray diffraction study the molecular structure of 3,7-dimethyl-9-thia-3,7-diazabicyclo[3.3.1]nonane-9,9-dioxide having a chair-chair conformation with a diequatorial arrangement of methyl groups at nitrogen atoms is determined. Compound 1 C₈H₁₆N₂O₂S crystallizes in the space group Pnma with the following cell parameters: a = 11.0262(3) Å, b = 14.4490(3) Å, c = 6.1780(3) Å.     

Development of a 9-borabicyclo[3.3.1]nonane-mediated solid-phase Suzuki coupling for the preparation of dihydrostilbene analogs

A novel 9-borabicyclo[3.3.1]nonane-mediated solid-phase Suzuki coupling was developed to generate dihydrostilbenes (bibenzyls) and related compounds. Using optimized conditions (20 mol% PdCl₂(dppf), 10 equiv. Et₃N, and 10 equiv. olefin/9-BBN, in 9:1 DMF/H₂O, 50°C, 18 h), high conversions to desired products were generally obtained. A small combinatorial library of derivatives was successfully prepared via radiofrequency tagging and directed sorting techniques.     

The reaction of B-alkyl-9-borabicyclo[3.3.1]nonanes with aldehydes and ketones. A facile elimination of the alkyl group by aldehydes

Certain B-alkyl-9-borabicyclo[3.3.1]nonanes (9-BBN) reduce benzaldehyde to benzyl alcohol under exceptionally mild conditions. Factors which contribute to a high rate of reaction include: an increase in the degree of substitution at the position β to the boron (isobutyl > 1-butyl >> ethyl), the ability of the alkyl group to form a syn-planar B—C—C—H conformation (cyclopentyl ? norbornyl > sec-butyl >> cyclohexyl), and the presence of an electron-withdrawing para-substituent on the benzaldehyde (p-Cl > p-H > p-CH₃O). The B-alkyl group is transformed into an olefin as the benzaldehyde is reduced. Elimination takes place predominantly if not exclusively towards the more highly substituted β hydrogen. The reaction obeys second order kinetics. The observations are consistent with a cyclic mechanism rather than a dehydroboration-reduction pathway.     

Silver-catalyzed [2,3]-rearrangement of halonium ylides derived from allyl and propargyl halides and alkyl diazoacetates

A silver(I) complex derived from a polyfluorinated tris(pyrazolyl)borate effectively catalyzes carbene transfer to allylic and propargylic halides, leading to the formation of alpha-haloacetate derivatives.     

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.     

Boron trifluoride etherate/halide ion,a novel reagent for the conversion of allyl,benzyl and tertiary alcohols to the halides

A combination of boron trifluoride etherate and halide ion is found to be an excellent reagent for the conversion of allyl, benzyl and tertiary alcohols to the halides.     

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.