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.

Don M. Coltart

http://fds.duke.edu/db/aas/Chemistry/faculty/don.coltart

Assistant professor, Duke
NSERC, AHFMR, and CRI Postdoctoral Fellow, Memorial Sloan-Kettering Cancer Center, 2001–2004
Ph.D. Chemistry, University of Alberta, 2000
M.S. Chemistry, University of Manitoba, 1995
B.S. Biochemistry, University of Manitoba, 1993

Research Interests

Asymmetric α-Alkylation of Ketones via Activated Hydrazones

Direct Carbon-Carbon Bond Formation via Soft Enolization of Thioesters

Natural Products Total Synthesis