Oxidative cleavage of α-hydroxyketones

Tetrahedron Letters 50 (2009) 5399–5402
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The oxidative cleavage of vicinal diols, a-hydroxyketones, and related functionalities is a common synthetic procedure and various reagents are available to perform this reaction, such as sodium bismuthate,1 iodo triacetate,2 manganic pyrophosphate,3 KHSO5,4 calcium hypochlorite,5 basic hydrogen peroxide,6 methylrhenium trioxide,7 Bi/O2,8 sodium percarbonate,9 and vanadium-based HPA and dioxygen.10 However, the most versatile reagents for this purpose are sodium metaperiodate,11 and lead tetraacetate.12–14
Usually sodium metaperiodate is used in aqueous solutions, because the effectiveness of this oxidant in organic solvents is very limited due to its insolubility.15 Lead tetraacetate has been used in non-aqueous media to accomplish the same types of reactions effected by periodates with water-soluble compounds.15 On the
other hand, this reagent is difficult to store and handle, non-environmentally friendly and, being more reactive, can afford undesired oxidation byproducts.
Aiming to expand the versatility of sodium metaperiodate as an oxidating reagent in organic media, and to overcome the solubilityissues, variations of a silica gel-supported sodium metaperiodate reagent have been disclosed, to promote oxidative cleavage of 1,2 diols, and oxidation of hydroquinones and sulfur-containing compounds.16–18 Usually the sodium periodate is adsorbed on silica gel, and stirred with the starting material in dichloromethane, ether, or benzene.
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One of the conditions described in the reference paper (NaIO4/SiO2/toluene) was applied to a mixture of alpha-hydroxyketone and TMS protected alpha-hydroxyketone shown below.
Surprisingly, only alpha-hydroxyketone was cleaved. The TMS protected alpha-hydroxyketone survived.
compared with HIO4 in Et2O, this condition (NaIO4/SiO2/toluene) is more neutral.

A Mask of the More Reactive Carbonyl

David Colby and co-workers from Purdue have just added a useful way to selectively reduce less reactive carbonyls (ie: lactone) over more reactive ones (ie:  ketone) by introducing N,O-dimethylhydroxylamine in the presence of an aluminum reducing agent (DIBAL).

deprotection of dimethyl acetal

1. in a particular substrate bearing a terminal double bond at 5,6 position related to the acetal,
the following deprotection methods failed

Methods tried:                                 results:

1. TFA/water/chloroform                   unknown product, aldehyde/alkene disappeared

2. I2/acetone                                     unknown product, aldehyde/alkene disappeared

3.HCOOH, pentane                          unknown product, aldehyde/alkene disappeared

4. TESOTf, 2,6-lutidine                       no reaction

the following method is successful:

DDQ/MeCN/water rt.

preparation of 2-Bromo-3-(trimethylsillyl)-1-propene

(2-Bromoallyl)trimethylsilane
Expensive.
two methods to prepare it.

1. coupling of 2,3-dibromopropene with a trimethylsilyl organocopper reagent generated by addition
of 1.5 equiv of cuprous cyanide to (trimethylsily1)lithium in a 3:l THF-HMPA mixture at 0 C.
2. Alternatively, the bromosilane was conveniently prepared according to eq 2 in 71% yield. This method has the advantage of avoiding the use of HMPA.

The resulting bromosilane can be distilled and stored in the dark for prolonged periods.

Reference:
J. Am. Chem. SOC. 1991, 113, 7350-7362.

synthesis of cyclopentanones

From:
An efficient one-pot method for the synthesis of mono- and biscyclopentenones via zirconium-catalyzed cycloalumination of cyclic alkynes and diynes, Tetrahedron Letters (2010), doi: 10.1016/j.tetlet.2010.08.120


Cyclopentenones have attracted the attention of organic chemists due to their wide use as building blocks in organic synthesis. In addition, they are often encountered in drugs and flavoring compounds.1

Efficient and widely used procedures for preparing cyclopentenones include the Nazarov cyclization, the
Pauson-Khand reaction and methods based on intramolecular cyclization of dienes, enynes and diynes
catalyzed by Ru, Ir, Rh, Au, Pd or Ni complexes.2
Another method for the synthesis of cyclopentenones
includes intramolecular carbocyclization of aluminacyclopentenes3 generated in situ in Zr-catalyzed
cycloalumination reactions of alkynes and Et3Al (Dzhemilev reaction),4 and their subsequent treatment with
CO2, ClCOOEt or CO(OEt)2.

reference:

1. (a) Surburg, H.; Panten, J. Common Fragrance and Flavor Materials: Preparation, Properties and Uses. Willey&Sons, 2006, pp. 330. (b) Hendrickson, J. B.; Palumbo, P. S. J. Org.Chem. 1985, 50, 2110. (c) Ceccherelli, P.; Curini, M.;Marcotullio, M. C.; Rosati, O.; Wenkert, E. J. Org. Chem.1990, 55, 311. (d) Conti, M. Anti-Cancer Drugs 2006, 17,1017.
2. (a) He, W.; Sun, X.; Frontier, A. J. J. Am. Chem. Soc. 2003,125, 14278. (b) Grant, T. N.; West, F. G. J. Am. Chem. Soc.2006, 128, 9348. (c) Shindo, M.; Yaji, K.; Kita, T.; Shishido,K.; Choueiry, D. Synlett 2007, 1096. (d) Saito, A.; Umakoshi,M.; Yagyu, N.; Hanzawa, Y. Org. Lett. 2008, 10, 1783. (e)Magnus, P. Tetrahedron Lett. 1985, 26, 4851. (f) Deng, L.-J.;Liu, J.; Hung, J.-Q.; Hud, Y.; Chen, M.; Lan, Y.; Chen, J.-H.;Lei, A.; Yang, Z. Synthesis 2007, 2565. (g) Park, K.H.; Song,S.U.; Chung, Y.K. Tetrahedron Lett. 2003, 44, 2827. (h)Shibata, T.; Toshida, N.; Yamasaki, M.; Maekawa, S.;Kagaki, K. Tetrahedron 2005, 61, 9974; (j) Rausch, B.;Gleiter, R. Tetrahedron Lett. 2001, 42, 1651; (k) Gleiter, R.;Schulte, J.H.; Werz, D.B. Eur. J. Org. Chem. 2004, 4077; (l)Oh, C.H.; Karmakar, S. J. Org. Chem. 2009, 74, 370.
3. Negishi, E.; Montchamp, J.-L.; Anastasia, L.; Elizarov, A.;Choueiry, D. Tetrahedron Lett. 1998, 39, 2503.
4. (a) Name Reactions and Reagents in Organic Synthesis.Mundy, B. P.; Ellerd, M. G.; Favaloro, F. G. Jr. Eds. Wiley-Interscience. New Jersey. 2005, pp. 882; (b) Dzhemilev, U.M. Tetrahedron 1995, 51, 4333. (c) Dzhemilev, U. M.Mendeleev Commun., 2008, 18, 1. (d) Dzhemilev, U. M.;Ibragimov, A. G. J. Organomet. Chem., 2010, 695, 1085. (e)D’yakonov, V. A. Dzhemilev Reaction in Organic and
Organometallic Synthesis, New-York.: NOVA Sci. Publ.,2010. p. 96.

activation of Magnesium for grignard reaction

Grignard: Initiating the reaction is the tricky part, people have used 1,2-dibromomethane, iodine, TMSCl - but for me the best working initiation technique is to place few equivalents of Mg turnings into an oven-dried flask with a large egg-shaped stirbar, flush it thoroughly with dry argon, add few drops of Br2 and dry-stir the Mg turnings in the Br2 vapors overnight. Then add freshly distilled ether solvent via canula (the bromine color disappears) and then carefully your substrate. I got some Grignards like BrMg(CH2)3MgBr by this technique that are hard to make by other methods (unless you want to mess with Rieke Mg). The Mg turnings are fairly fragile and crushing them in oxygen-free and nitrogen-free environment uncovers a highly-reactive newly-formed surface which is further protected by MgBr2 formation. MgBr2 is soluble in ether. Please note that one has to use Ar because N2 reacts with fresh Mg surfaces, to produce dark Mg nitride.


http://chemknowhow.com/forum/viewtopic.php?t=448

Prepartion of magnesium bromide diethyl etherate solution

Once I was going to make a MgBr2-OEt2 1M solution in Ether.
When the ether was added into MgBr2-OEt2 powder, two layers of liquid was resulted.

Turned out the button layer contains MgBr2 at 39%wt. the top layer contains 3%wt.
addition of some benzene can increase the solubility and make a clear solution.

reference:
digital.library.okstate.edu/OAS/oas_pdf/v32/p79_82.pdf

note:
In a preparation, 1.5 M clear solution was made using 27 ml of Et2O and 4 mL of benzene at 25 C.