making of diazotransfer reagents

ex. 2,4,6-triisopropylbenzenesulfonyl azide

1. reaction can be monitored by TLC. the azide is slightly less polar than the sulfonylchloride.

2. detailed reaction:
1. dissolve the tipscl in acetone.
2. add NaN3 into the reaction mixture. vigrous stirring for at least 20 min. NaN3 can't dissolve, a cloudy solution.
3. add water dropwise into the solution, until clear.
4. 1 hr, st gone.
5. wash with water, extracted into ether. dried, concentrated. sticky oil.
6. can be recrystallized in hexanes.

Note: if water was added at the very beginning, reaction can't go because tipscl can't dissolve in water.

Drying reagents MgSO4 vs. Na2SO4

MgSO4 is more expansive, but as a drying reagent, it is much quicker and more complete than Na2SO4.
when a lot of water is present, MgSO4 generates heat, Na2SO4 does not.

petasis reagent: (cp)2Ti(cyclopropane)2

Cp2Ti(cyclopropane)2 is used to convert a ketone into cyclopropane-alkene.

1. making of this reagent.
Li,Et2O, 0 C, add cyclopropanebromide dropwise into the solution.( very exothermic).
low sodium Li can be used. 1hr at rt, then the solution was transfered into a Et2O solution of Cp2TiCl2 at 0 C. stirred for 90 min, quenched by ice water. washed, dried over MgSO4, concentrated. red solid. dissolved in toluene (0.5-0.8 mol/l). The solubility is poor in toluene, so can't make more concentrated). stored in freezer. Solid will be precipitated from the solution in the freezer, so warm it up before use.

2. reaction.
usually, 3-5 eq. of the reagent, toluene as solvent, 50-55C. overnight.
the product is very easy to isomerize to other alkene-isomers. So during the reaction, some NaHCO3 solid can bee added to prevent isomerization.

Diastereoselective Intermolecular Pauson-Khand Reactions of Chiral Cyclopropenes

Joesph M. Fox of University of Delaware.

1. the unusual reactivity of cyclopropenes can increase the scope and utility of intermolecular Pauson-Khand reactions.
2. The well-defined chiral environment of cyclopropenes has a powerful influence on the diastereoselectivity of the reactions
and leads to the production of a single cyclopentenone in each of the described cases.
3. The cyclopropane ring strongly influences the stereochemistry of reactions at the enone
4. the three-membered ring can subsequently be cleaved under mild conditions.

5. Notably, the types of products that are accessible via cyclopropene Pauson- Khand/reductive cleavage complement those that can be formed using directed Pauson-Khand methodology
.

Pd-Catalyzed alpha-Arylation of Trimethylsilyl Enol Ethers with Aryl Bromides and Chlorides

By John F. Hartwig, Angewandte Chemie International Edition, 2006, 5852-5855

1. these conditions allow the coupling of bromoarenes with functionalities that are not tolerated by the basic alkali-metal enolates.

2. Entry 3, 6 showed this method has very good regioselectivity.