Titanium‐Mediated Carboxylation of Alkynes With Carbon Dioxide

Abstract

The regioselective carboxylation of nonactivated internal alkynes can be performed with carbon dioxide under atmospheric pressure using a simple procedure based on the chemistry of Sato‐type diisopropyloxytitanacyclopropenes. Various polysubstituted vinylcarboxylic acids and butenolides can be prepared in this way. In addition, this paper describes an experimental protocol for the preparation of solutions of (η2‐cyclopentene)diisopropyloxytitanium. This complex also reacts with carbon dioxide, and mediates pinacol coupling of acetophenone. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Radical substitution with azide: TMSN3–PhI(OAc)2as a substitute of IN3

“…24 To a solution of 4-benzyloxybut-1-ene (5.13 g, 31.6 mmol) in 280 ml THF-H 2 O (4 : 3) was added NaIO 4 (14.9 g, 67.7 mmol). 4-Benzyloxybut-1-ene (24a) was prepared in a 92% yield according to the protocol of Six.…”

Development of a double allylboration reagent targeting 1,5-syn-(E)-diols: application to the synthesis of the C(23)–C(40) fragment of tetrafibricin

“…The synthesis of aldehyde 4 began with cross-metathesis between readily available olefin 54 40 and acrolein in the presence of Grubbs-Hoveyda second-generation catalyst. 39 This reaction provided the unsaturated aldehyde 55 in 85% yield.…”

“…To a solution of alkene 54 40 (3.12 g, 16.2 mmol) in CH 2 Cl 2 (70 mL) under argon, were successively added acrolein (freshly distilled, 3.25 mL, 48.7 mmol) and Hoveyda-Grubbs 2 nd generation catalyst 39 (weighed in a glove box, 254 mg, 0.40 mmol) as a solution in CH 2 Cl 2 (3 mL). The reaction mixture was stirred overnight at room temperature, then directly concentrated in vacuo .…”

Low-Valent Titanium-Mediated Reductive Coupling of Carbonyl Compounds

“…The crystallographically characterized monomeric noncyclopentadienyl Ti(III) complex TiCl 3 (TMEDA)(THF) (10) efficiently coupled aromatic aldehydes under mild conditions to give 1,2-diols in good to excellent yields and with high dldiastereoselectivities (dl:meso > 94:6) [50]; this reagent readily tolerated ether, halide, cyano, and ester groups bound to aromatic rings. Reductive coupling of acetophenone by (η 2 -cyclopentene)diisopropyloxytitanium (11) was recently shown to afford 2,3-diphenyl-butane-2,3-diol in 59% isolated yield with a dl:meso ratio of 78:22 [51]. All of these studies have served to confirm substantial effects of the structure of low-valent titanium species on the chemo-and stereoselectivity of pinacol coupling reaction.…”