BESTMAN-OHIRA REAGENT

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7. The Seyferth–Gilbert homologation is a chemical reaction of an aryl ketone 1 (or aldehyde) with dimethyl (diazomethyl)phosphonate 2 and potassium tert-butoxide to give substituted alkynes 3.^[1][2] Dimethyl (diazomethyl)phosphonate 2 is often called the Seyferth–Gilbert reagent.^[3]
   
   
   This reaction is called a homologation because the product has exactly one additional carbon more than the starting material.
   
   

   Reaction mechanism

   Deprotonation of the Seyferth–Gilbert reagent A gives an anion B, which reacts with the ketone to form the oxaphosphetane D. Elimination of dimethylphosphate E gives the vinyl diazo-intermediate Fa and Fb. The generation of nitrogen gas gives a vinyl carbene G, which via a 1,2-migration forms the desired alkyne H.
   
   

   Bestmann modification

   Ohira–Bestmann reagent

   Names
   IUPAC name dimethyl (1-diazo-2-oxopropyl)phosphonate
   Identifiers
   CAS Number	90965-06-3
   ChemSpider	9281325
   Jmol interactive 3D	Image
   PubChem	11106189
   InChI[show]
   SMILES[show]
   Properties
   Chemical formula	C5H9N2O4P
   Molar mass	192.11
   Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
   Infobox references

   Dimethyl (diazomethyl)phosphonate can be generated in situ from dimethyl-1-diazo-2-oxopropylphosphonate (also called the Ohira-Bestmann reagent) by reaction with methanol and potassium carbonate. Reaction of Bestmann's reagent with aldehydes gives terminal alkynes often in very high yield.^[4][5]
   
   
   The use of the milder potassium carbonate makes this procedure much more compatible with a wide variety of functional groups.
   

   Improved in situ generation of the Ohira-Bestmann reagent

   
   
   Safe and scalable synthesis of alkynes from aldehydes
   Recently a safer and more scalable approach has been developed for the synthesis of alkynes from aldehydes. This protocol takes advantage of a stable sulfonyl azide, rather than tosyl azide, for the in situ generation of the Ohira−Bestmann reagent.^[6]
   Another modification for less reactive aldehydes is made by replacement of potassium carbonate with caesium carbonate in MeOH and results in a drastic yield increase.^[7]
   
   

   References

   1. 
      
8. D. Seyferth, R. S. Marmor and P. Hilbert (1971). "Reactions of dimethylphosphono-substituted diazoalkanes. (MeO)2P(O)CR transfer to olefins and 1,3-dipolar additions of (MeO)2P(O)C(N2)R". J. Org. Chem. 36 (10): 1379–1386. doi:10.1021/jo00809a014.
9. 
   
10. J. C. Gilbert and U. Weerasooriya (1982). "Diazoethenes: their attempted synthesis from aldehydes and aromatic ketones by way of the Horner-Emmons modification of the Wittig reaction. A facile synthesis of alkynes". J. Org. Chem. 47 (10): 1837–1845. doi:10.1021/jo00349a007.
11. 
    
12. D. G. Brown, E. J. Velthuisen, J. R. Commerford, R. G. Brisbois and T. H. Hoye (1996). "A Convenient Synthesis of Dimethyl (Diazomethyl)phosphonate (Seyferth/Gilbert Reagent)". J. Org. Chem. 61 (7): 2540–2541. doi:10.1021/jo951944n.
13. 
    
14. S. Müller, B. Liepold, G. Roth and H. J. Bestmann* (1996). "An Improved One-pot Procedure for the Synthesis of Alkynes from Aldehydes". Synlett 1996 (06): 521–522. doi:10.1055/s-1996-5474.
15. 
    
16. G. Roth, B. Liepold, S. Müller and H. J. Bestmann (2004). "Further Improvements of the Synthesis of Alkynes from Aldehydes". Synthesis 2004 (1): 59–62. doi:10.1055/s-2003-44346.
17. 
    
18. Jepsen, T.H, Kristensen, J.L. J. Org. Chem. 2014, "In Situ Generation of the Ohira–Bestmann Reagent from Stable Sulfonyl Azide: Scalable Synthesis of Alkynes from Aldehydes". http://pubs.acs.org/doi/abs/10.1021/jo501803f
19. 
    
Lidija Bondarenko, Ina Dix, Heino Hinrichs, Henning Hopf* (2004). "Cyclophanes. Part LII:1 Ethynyl[2.2]paracyclophanes – New Building Blocks for Molecular Scaffolding". Synthesis 2004 (16): 2751–2759. doi:10.1055/s-2004-834872.

Can Tho, Vietnam

Can Tho

City in Vietnam

Can Tho is a city in southern Vietnam’s Mekong Delta region. Set on the southern bank of the Hau River, it’s known for its network of canals and nearby floating markets. The modern, cable-stayed Can Tho Bridge spans the river. The busy Ninh Kiều waterfront is a hub for boat trips on the waterways surrounding the city.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Can Tho,  Can Tho, my country, is waiting for us.  Mom and her friends want to see where I live and work.  The speedboat being back in service, we get to Can Tho in 4 hours. The next day, boat trip on the arroyos of course, with the traditional stop in the fruit garden around a good table.

Going around in the rice fields, after lunch...

And in Can Tho's market after going back to town.

The street children shelter Interests the Daltons a lot, but that's not surprising : it's a wonderful place.  Yen (right on the picture) takes daily care  of about 92 kids, of which about 50 stay there permanently.  Among them, about 20 orphans. A roof (and a bed !), meals, education (basic and professional), counseling : Yen and her staff are there !

We (the Daltons) set up a budget, out of which I regularly take the money Yen asks for (mostly for medications).

The Daltons at school For the great pleasure of the teachers (two with us on the picture), the principal, but mostly of the kids ! Those were a lot shyer than usual though, having 4 French-speaking guests in the classrooms being quite rare !

And voilà...

The Daltons split up again, Averell staying in Can Tho (all holidays come to an end...).  After the others left in a minibus to Saigon, I went back to work...

 

 

 

 

 

 

 

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