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description=3 posts published by milkshake during August 2007;

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august 2007 org prep daily org prep daily august 26 2007 one phosphine to rule them all filed under lit highlights milkshake 10 20 am buchwald et al angew chem int ed eng 45 39 6523 7 2006 doi 10 1002 anie 200601612 buchwald group developed a number of biphenyl based phosphine ligands useful for pd 0 catalyzed arylations descendants from binap these ligands form 1 1 complexes with pd 0 that are particularly active catalysts allowing arylations with both poor electrophiles unactivated aryl chlorides and lazy nucleophiles such as heterocycles with very acidic nh the reason why the bulky monodentate electrone rich 2 biphenyl phosphines are good is that they make pd 0 more nucleophilic which helps the pd insertion into ar x while the bulk promotes the fast migration dissociation rates in the intermeditate complexes and the formation of pdl2 is supressed even a very sterically hindered pdl complex is coordinationally less saturated and hence more reactive than a pdl2 complex with a less bulky ligand pdl4 is worse still the pi electrons of the second benzene ring donate to pd and the ring shielding prevents pdl2 from happening one of the problems with aryl based phosphines has been cyclometallation the palladacycles such as hermann catalyst are good for high temperature heck reactions but are quite inert below their decomposition temperature in this case the cyclometallation is prevented by the ortho isopropyl groups there are other good phosphine ligands useful for difficult arylations xanphos 1 tert bu3p 2 and josiphos 3 the great advantage of buchwald phosphine ligands is that they are perfectly air stable highly crystalline solids easy to make and the produced catalysts are pretty active and robust this newest ligand with isopropyls on the ring and tert butyls on the phosphine is reported to be very good for arylation of poorly reactive n nucleophiles with pd2 dba 3 as a pd source and naotbu in toluene at 80c or cs2co3 in dioxane at 100c and some functional groups can be even left unprotected such as primary amide and phenol without interfering with the arylation process i have tried this ligand with my substrates and aryl bromindes and nearly everything that i did worked on the first try with 2 5 of pd loadings and naotbu in toluene at 80c the only exception was arylation using aryl iodide as an electrophile i suspect that the generated iodide anion complexed to pd and prevented the catalyst from turning over but all my aryl bromides worked beautifully the ligand is available from aldrich 638080 5g and it is not too cheap 161 5g so it would be worth making your own ligand for large scale experiments the phosphine can be made in a one pot reaction from commercial reactants note 1 cheap but often needs high temperature and a high boiling solvent like o dichlorobenzene best to be used 1 1 with pd 0 since pd xanphos 2 is inert note 2 expensive the free tbu3p is super air sensitive and should be handled only in glove box it likes to smolder on air use the air stable tetrafluoroborate salt tert bu3 ph bf4 instead 2 1 with pd 0 note 3 josiphos is a chiral ligand very expensive comments 11 august 20 2007 2 2 bromophenylamino thiazole 4 carboxylic acid filed under procedures milkshake 8 38 pm 2 bromophenyl isothiocyanate 1 0ml 1 593g 7 44 mmol was added dropwise into a stirred 7m anh nh3 solution in methanol 40ml the mixture was stirred for 1 hour and then evaporated the residue was dissolved in ethanol 25ml heated to reflux cooled filtered from a small amount of cloudy precipitate and the filtrates were evaporated the residue was induced to crystallization by addition of few drops of water the solidified mass was dried on highvac the obtained crude thiourea 1 737 g of a light tan crystalline solid was dissolved in ethanol 50 ml with a gentle heating the solution was cooled to rt and solid bromopyruvic acid 1 242g 7 44 mmol was added the mixture was stirred for 30 min and then evaporated the residue was suspended in water 50ml with sonication for 10 min anhydrous sodium acetate solid 840mg was added to raise the ph of the mixture and the slurry was sonicated for additional 5 min the precipitated product was collected by filtration washed with water dried by suction and then on highvac y 1 749g 78 5 of a white crystalline solid 1h nmr d6 dmso 400mhz 12 681 very br s 1h 9 629 very br s 1h 8 144 dd 8 2hz 1 6hz 1h 7 718 s 1h 7 652 dd 8 0hz 1 5hz 1h 7 394 m 1h 7 039 m 1h lc ms esi 299 301 using the same procedure 1 0ml of 2 chlorophenyl isothiocyanate 1 310g 7 72mmol and 40ml of 7m methanolic nh3 provided 1 452g of a crude thiourea that was cyclized with bromopyruvic acid 1 289g 7 72 mmol and neutralized with acona 900mg to provide 1 401g 71 of 2 2 chlorophenylamino thiazole 4 carboxylic acid as a white crystalline solid 1h nmr d6 dmso 400mhz 12 705 very br s 1h 9 779 very br s 1h 8 358 dd 8 3hz 1 5hz 1h 7 748 s 1h 7 477 dd 8 0hz 1 4hz 1h 7 350 m 1h 7 070 m 1h lc ms esi 255 257 comments 5 august 16 2007 so many carbonyls so little use filed under mechanisms milkshake 4 12 pm lately i have been enjoying the pleasures of 3 5 diketoesters the effort turned out to be a complete waste of time but the joy of cyclization priceless comments 4 pages about milkshake about org prep daily bug report chemistry resources chemistry chemjobber in the pipeline med chemist open flask org chem portal practical fragments stellen fuer chemiker edible links serious eats links to behold idle words categories chris douglas industry life krest17 lab destruction lit highlights mechanisms procedures questions uncategorized search archives january 2026 december 2025 november 2025 october 2025 september 2025 april 2019 march 2019 december 2018 june 2018 september 2017 august 2017 march 2016 october 2015 august 2015 july 2015 june 2015 march 2015 november 2014 july 2014 may 2014 september 2013 july 2013 may 2013 april 2013 october 2012 september 2012 august 2012 january 2012 december 2011 november 2011 october 2011 july 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