Alpine borane: Difference between revisions

{{Chembox

| Verifiedfields = changed

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| verifiedrevid = 417932141

| Reference = <ref>[http://www.sigmaaldrich.com/catalog/ProductDetail.do?N4=417203|ALDRICH&N5=SEARCH_CONCAT_PNO|BRAND_KEY&F=SPEC ''R''-Alpine-Borane] and [http://www.sigmaaldrich.com/catalog/ProductDetail.do?N4=417041|ALDRICH&N5=SEARCH_CONCAT_PNO|BRAND_KEY&F=SPEC ''S''-Alpine-Borane] at [[Sigma-Aldrich]]</ref>

| ImageAlt = Skeletal formula of alpine borane

| ImageFile1 = Alpine-borane-3D-balls.png

| ImageAlt1 = Ball-and-stick model of the alpine borane molecule

|Section1={{Chembox Identifiers

| PubChem = 9921373

| PubChem_Comment = R

| PubChem1 = 10890567

| PubChem1_Comment = S

| CASNo_Ref = {{cascite|correct|??}}

| CASNo1_Ref = {{cascite|correct|??}}

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|Section2={{Chembox Properties

| C=18 | H=31 | B=1

| Density = 0.947 g/mL

| MeltingPt =

| BoilingPt= >

| BoilingPtC = 55

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|Section7={{Chembox Hazards

| GHSPictograms = {{GHS02}}

| GHSSignalWord = Danger

| HPhrases = {{H-phrases|250}}

| PPhrases = {{P-phrases|210|222|280|302+334|370+378|422}}

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|Section8={{Chembox Related

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'''Alpine borane''' is the commercial name for an [[organoboron compound]] that is used in [[organic synthesis]]. It is a colorless liquid, although it is usually encountered as a solution. A range of alkyl-substituted borane are specialty reagents in organic synthesis. Two such reagents that are closely related to Alpine borane are [[9-BBN]] and [[diisopinocampheylborane]].

==Preparation and reactions==

:[[File:Synthesis of (R)-Alpine Borane.png|center|500x500px]]

This [[reagent]] is generated by treating [[9-Borabicyclo(3.3.1)nonane|9-BBN]] with [[α-pinene]].<ref name=CR>{{cite journal | title = Asymmetric reductions with organoborane reagents | author = M. M. Midland | journal = Chemical Reviews | year = 1989 | volume = 89 | issue = 7 | pages = 1553–1561 | doi = 10.1021/cr00097a010}}</ref>

This sterically crowded [[Chirality (chemistry)|chiral]] trialkylborane can [[stereoselective]]ly reduce aldehydes in what is known as the '''Midland Alpine borane reduction''', or simply the Midland reduction.<ref>M. Mark Midland "B-3-Pinanyl-9-borabicyclo[3.3.1]nonane" in Encyclopedia of Reagents for Organic Synthesis 2001 John Wiley, New York.{{doi|10.1002/047084289X.rp173}}. Article Online Posting Date: April 15, 2001</ref>

:C₈H₁₂B-pinanyl + RCDO → C₈H₁₂BOCHDR + (+)-''d''-pinene

:C₈H₁₂BOCHDR + H₂O → C₈H₁₂BOH + HOCHDR

It is also effective for the stereoselective reduction of certain acetylenic ketones.<ref>{{cite journal |year=1985| first1 = M. Mark|last1=Midland|first2= Richard S.|last2=Graham | title =Asymmetric Reduction of α,β-Acetylenic Ketones with ''B''-3-Pinanyl-9-Borabicyclo[3.3.1]nonane: (R)-(+)-1-Octyln-3-ol | volume = 63 | page = 57 | doi = 10.15227/orgsyn.063.0057|journal=Organic Syntheses}}</ref> The reaction is proposed to involve formation of an adduct by coordination of the carbonyl oxygen to boron. Intramolecular hydride transfer from the pinane substituent to the carbonyl carbon ensues. Many substrates for the Midland reduction have a low steric group such as an alkyne<ref>''Intramolecular Arene-Alkyne Photocycloaddition'' M. C. Pirrung [[J. Org. Chem.]]; '''1987'''; 52(8); pp 1635 - 1637; {{doi|10.1021/jo00384a057}}</ref> or a nitrile<ref> {{cite journal|doi=10.1021/jo00217a053 |title=Efficient Asymmetric Reduction of Acyl Cyanides with B-3-Pinanyl 9-BBN (Alpine-Borane) |date=1985 |last1=Midland |first1=M. Mark |last2=Lee |first2=Penny E. |journal=The Journal of Organic Chemistry |volume=50 |issue=17 |pages=3237–3239 }}</ref> so as to increase selectivity. Stereochemical control comes from coordination of the carbonyl bulky borane, followed by hydride transfer opposite the largest group.<ref name=CR/><ref name="Li">

{{cite book

| author = Li, J. J.

| title = Name Reactions, A Collection of Detailed Mechanisms and Synthetic Applications

| url = https://archive.org/details/namereactions00jjli

| url-access = limited

| publisher = Springer

| year = 2009|edition=4th

| location = New York, New York

| pages = [https://archive.org/details/namereactions00jjli/page/n376 359]–360

| isbn = 978-3-642-01052-1 }}</ref>

[[File:Midland reduction transition state.png|center|840x840px]]

==See also==

{{Portal|Chemistry}}

* [[Corey-Itsuno reduction]]

* [[Asymmetric hydrogenation]]