Thursday, August 26, 2010

Synthesis of Arylboronic Acid Ester


General Procedure for the Synthesis of Arylboronic acid ester from Arylboroic Acid with 2,2-Dimethyl-1,3-propanediol (5 mmol scale).


In a 50ml flask equipped with a stir-bar, arylboroic acid (5 mmol) and 2,2-dimethyl-1,3-propanediol (6 mmol) were combined. 15 mL dimethyl ether was added to the flask and the solution was stirred for 6 hours under room temperature. The dimethyl ether was then removed under vacuum to get the white solid mixture. The mixture was washed three times with water to remove the excess 2,2-dimethyl-1,3-propanediol. The product was dried at 50 under vacuum.
This method gave quantitative yield for 3 g scale.

Friday, August 20, 2010

Synthesis of Phenanthrone Derivatives from sec-Alkyl Aryl Ketones and Aryl Halides via a Palladium-Catalyzed Dual C−H Bond Activation and Enolate Cyclization - Journal of the American Chemical Society (ACS Publications)



Abstract Image
A palladium-catalyzed chelation-assisted C−H activation of alkyl aryl ketones and their reaction with aryl iodides to afford ortho-arylated products is described. For sec-alkyl aryl ketones, the catalytic reaction proceeds further to give 10,10-dialkylphenanthrone derivatives. A possible reaction mechanism involving directed dual C−H bond activation and enolate cyclization for the formation of 10,10-dialkylphenanthrone derivatives is proposed.

Tuesday, August 17, 2010

Non-metal-catalysed C-C coupling

Non-metal-catalysed C-C coupling

Chinese chemists have successfully coupled aromatic molecules without the use of a transition metal catalyst - something that people have been trying to do for years with little success. Such cross-coupling reactions are crucial to organic synthesis and typically require expensive metals such as palladium. Efforts to find cheaper and more widely available alternatives have proved challenging.

Now, Wei Liu, from Wuhan University, and colleagues appear to have succeeded by using an organic catalyst, DMEDA (N,N'-dimethylethane-1,2-diamine) in the presence of the base potassium tert-butoxide. The team coupled unactivated benzene with a range of aryl iodides in the presence of the organic catalyst and the base.

"We have checked for contamination and excluded the involvement of trace amounts of transition metals" - Aiwen Lei, Wuhan University

The researchers suggest that the reaction proceeds via the formation of a radical, with the potassium salt initiating radical formation in the presence of DMEDA. 'In radical trap experiments the coupling was inhibited by a classical radical scavenger which suggested that radical species are involved,' says team member Aiwen Lei.

Could trace amounts of transition metal have contaminated the experiment? 'Obviously this is one of the most important factors,' says Lei. 'We have checked the contamination of trace amounts of transition metals by ICP [inductively coupled plasma atomic emission spectroscopy] and excluded the involvement of small amounts of transition metals in this transformation.' In addition, the potassium tert-butoxide used in the work was purified by sublimation to remove any contaminants.

Lei believes that the work could herald a new direction in organic synthesis. 'This is the first report of organocatalysis in carbon-carbon coupling or direct arylation between aryl halides and arenes, which could be considered as a conceptually different approach towards biaryl syntheses.'

Commenting on the work, Carsten Bolm, an organic synthesis expert from Aachen University in Germany, says, 'To be able to prepare cross-coupling products without the use of transition metals is an important scientific advance. Although at the present stage the substrate scope is by far too limited to make the process synthetically attractive, the findings illustrate that new reaction paths in direct C-H arylations are still to be discovered, and as such this work will be highly stimulating to the community.'

Wednesday, August 11, 2010

Characteristic IR Band Positions


Characteristic IR Band Positions
 GroupFrequency Range (cm-1)
OH stretching vibrations  
  Free OH3610-3645 (sharp)
  Intramolecular H bonds3450-3600 (sharp)
  Intermolecular H Bonds3200-3550 (broad)
  Chelate Compounds2500-3200 (very broad)
NH Stretching vibrations  
  Free NH3300-3500
  H bonded NH3070-3350
CH Stretching vibrations  
  =-C-H3280-3340
  =C-H3000-3100
  C-CH32862-2882, 2652-2972
  O-CH32815-2832
  N-CH3 (aromatic)2810-2820
  N-CH3 (aliphatic)2780-2805
  CH22843-2863,2916-2936
  CH2880-2900
SH Stretching Vibrations  
  Free SH2550-2600
C=-N Stretching Vibrations  
  Nonconjugated2240-2260
  Conjugated2215-2240
C=-C Stretching Vibrations  
  C=-CH (terminal)2100-2140
  C-C=-C-C2190-2260
  C-C=-C-C=-CH2040-2200
C=O Stretching Vibrations  
  Nonconjugated1700-1900
  Conjugated1590-1750
  Amides~1650
C=C Sretching Vibrations  
  Nonconjugated1620-1680
  Conjugated1585-1625
CH Bending Vibrations  
  CH21405-1465
  CH31355-1395, 1430-1470
C-O-C Vibrations in Esters  
  Formates~1175
  Acetates~1240, 1010-1040
  Benzoates~1275
C-OH Stretching Vibrations  
  Secondary Cyclic Alcohols990-1060
CH out-of-plane bending vibrations
   in substituted ethylenic systems
  
  -CH=CH2905-915, 985-995
  -CH=CH-(cis)650-750
  -CH=CH-(trans)960-970
  C=CH2885-895
    
Characteristic IR Absorption Frequencies of Organic Functional Groups
Functional Group
Type of Vibration
Characteristic Absorptions (cm-1)
Intensity
Alcohol
O-H
(stretch, H-bonded)
3200-3600
strong, broad
O-H
(stretch, free)
3500-3700
strong, sharp
C-O
(stretch)
1050-1150
strong
Alkane
C-H
stretch
2850-3000
strong
-C-H
bending
1350-1480
variable
Alkene
=C-H
stretch
3010-3100
medium
=C-H
bending
675-1000
strong
C=C
stretch
1620-1680
variable
Alkyl Halide
C-F
stretch
1000-1400
strong
C-Cl
stretch
600-800
strong
C-Br
stretch
500-600
strong
C-I
stretch
500
strong
Alkyne
C-H
stretch
3300
strong,sharp
stretch
2100-2260
variable, not present in symmetrical alkynes
Amine
N-H
stretch
3300-3500
medium (primary amines have two bands; secondary have one band, often very weak)
C-N
stretch
1080-1360
medium-weak
N-H
bending
1600
medium
Aromatic
C-H
stretch
3000-3100
medium
C=C
stretch
1400-1600
medium-weak, multiple bands
Analysis of C-H out-of-plane bending can often distinguish substitution patterns
Carbonyl
C=O
stretch
1670-1820
strong
(conjugation moves absorptions to lower wave numbers)
Ether
C-O
stretch
1000-1300 (1070-1150)
strong
Nitrile
CN
stretch
2210-2260
medium
Nitro
N-O
stretch
1515-1560 & 1345-1385
strong, two bands

IR Absorption Frequencies of Functional Groups Containing a Carbonyl (C=O)
Functional Group
Type of Vibration
Characteristic Absorptions (cm-1)
Intensity
Carbonyl
C=O
stretch
1670-1820
strong
(conjugation moves absorptions to lower wave numbers)
Acid
C=O
stretch
1700-1725
strong
O-H
stretch
2500-3300
strong, very broad
C-O
stretch
1210-1320
strong
Aldehyde
C=O
stretch
1740-1720
strong
=C-H
stretch
2820-2850 & 2720-2750
medium, two peaks
Amide
C=O
stretch
1640-1690
strong
N-H
stretch
3100-3500
unsubstituted have two bands
N-H
bending
1550-1640
Anhydride
C=O
stretch
1800-1830 & 1740-1775
two bands
Ester
C=O
stretch
1735-1750
strong
C-O
stretch
1000-1300
two bands or more
Ketone
acyclic
stretch
1705-1725
strong
cyclic
stretch
3-membered - 1850
4-membered - 1780
5-membered - 1745
6-membered - 1715
7-membered - 1705
strong
,-unsaturated
stretch
1665-1685
strong
aryl ketone
stretch
1680-1700
strong

A good general reference for more detailed information on interpretation of infrared spectra (as well as other spectroscopic techniques) is Silverstein, R.M.; Bassler, G.C.; and Morrill, T.C.Spectrometric Identification of Organic Compounds. 4th ed. New York: John Wiley and Sons, 1981. QD272.S6 S55