J. Michael Chong

Titration of alkyllithiums with a simple reagent to a blue endpoint

Abstract Reaction of readily available N-benzylbenzamide (1) with a slight excess of BuLi produces a deep blue dianion. Under suitable conditions (THF, −40°C), 1 may be used as a stoichiometric reagent to titrate n-BuLi, s-BuLi, and t-BuLi with good precision. Less reactive alkyllithiums (MeLi and MeLi·LiBr), aryllithiums, and LDA may be titrated at higher temperatures (−20 to 0°C). Titres are comparable to those obtained using the Gilman double titration method, and there appears to be no interference from alkoxides.

Observations on Sn-Li exchange in α-aminoorganostannanes and the configurational stability of non-stabilized α-aminoorganolithiums

Abstract α-Aminoorganostannanes undergo Sn-Li exchange to form carbanions which may be trapped with electrophiles if the amine moiety contains a methoxyethyl group. The α-aminoorganolithiums formed are configurationally stable for short times at low temperatures.

The Use of Phosphine Ligands to Control the Regiochemistry of Pd-Catalyzed Hydrostannations of 1-Alkynes: Synthesis of (E)-1-Tributylstannyl-1-alkenes

The regiochemistry of palladium-catalyzed hydrostannations of terminal alkynes is dramatically influenced by ligand effects. Use of phosphines such as Cy3P, t-Bu2PCH2t-Bu, and t-Bu3P provides (E)-1-tributylstannyl-1-alkenes with regioselectivities up to >99:<1 for substrates where the commonly used Ph3P shows much lower regioselectivities.

Alkylation of 1-alkynes in THF

Alkynes may be easily alkylated by sequential treatment with n-BuLi followed by an alkyl halide in THF. Primary iodides give excellent yields (75–99%) as do bromides in the presence of catalytic amounts of Bu4NI or NaI; in the absence of an iodide source, bromides react poorly. This method offers advantages over existing methods which use HMPA or NH3 as co-solvents.

Asymmetric synthesis of trans-2,5-diphenylpyrrolidine: A C2-symmetric chiral amine

Abstract (R,R)-2,5-Diphenylpyrrolidine of high enantiomeric purity (>98% e.e.) may be prepared from 1,4-diphenyl-1,4-butanedione in 4 steps and 64% overall yield. A key step is asymmetric reduction of the dione with Ipc2BCl.

Preparation of enantiomerically enriched α-hydroxystannanes via enzymatic resolution

Abstract The porcine pancreatic lipase (PPL) catalyzed esterifications of α-hydroxystannanes RCH(OH)SnMe 3 (R = Me, Et) and MeCH(OH)SnEt 3 with 2,2,2-trifluoroethyl valerate afford good yields and excellent enantiomeric (>95% ee) purities of the (S)-valerate and the (R)-α-hydroxystannane.

Reactions of α-epoxysilanes with organocopper reagents. A stereoselective route to alkenes

Abstract Reactions of α-epoxysilanes with cuprate reagents can be controlled to give β-silyl alcohols as major products. An oxidation, Grignard addition, and elimination sequence then provides alkenes with up to 98% de.

A route to enantiomerically-enriched α-silyl aldehydes from 2,3-epoxy alcohols

Abstract Asymmetric epoxidation of ( E )-3-trialkylsilyl-2-propen-1-ols gives the expected epoxides with high enantioselectivity. Ring opening reactions of these epoxides with organocopper reagents furnishes 1,2-diols which are readily cleaved with Pb(OAc) 4 to afford α-silyl aldehydes with no detectable loss of stereochemistry.

Regioselective reduction of 2,3-epoxy alcohol derivatives. An efficient route to enantiomerically pure 2-alkanols

Abstract Reduction of 2,3-epoxy tosylates with DlBAL-H provides high yields of 2-alkanols.

Chemoselective reduction of 2,3-epoxy tosylates with DIBAL-H as a general route to enantiomerically-enriched 1-tosyloxy-2-alkanols

Abstract 2,3-Epoxy tosylates may be reduced with DIBAL-H in CH 2 Cl 2 or ether at −40 °C to 1-tosyloxy-2-alkanols in high (94–98%) yields.