Synthetic studies on palytoxin stereocontrolled practical synthesis of the C.23 – C.37 segment

Tetrabutylammonium fluoride (TBAF)-catalyzed addition of substituted trialkylsilylalkynes to aldehydes, ketones, and trifluoromethyl ketones

Herein we report that tetrabutylammonium fluoride (TBAF) is a very efficient catalyst for the addition of trialkylsilylalkynes to aldehydes, ketones, and trifluoromethyl ketones in THF solvent at room temperature. The reaction conditions are mild and operationally simple, and a variety of aryl functional groups, such as chloro, trifluoromethyl, bromo, and fluoro groups, are tolerated. Impressively, using our protocol, useful CF(3)-bearing tertiary propargylic alcohols can be synthesized. Product yields are generally better than or comparable to those in the literature. 1-Phenyl-2-trimethylsilyl acetylene, trimethyl ((4-(trifluoromethyl)phenyl)ethynyl)silane, 1-trimethylsilyl-1-hexyne, and trimethyl(thiophen-3-ylethynyl)silane underwent clean conversion to their corresponding propargylic alcohols as products under our conditions. Heterocyclic carbonyl compounds, such as furan-3-carboxaldehyde, thiophene-3-carboxaldehyde, and 2-pyridyl ketone, gave good yields of propargylic alcohols.

Synthesis of functionalized diarylmethanes via a copper-catalyzed cross-coupling of arylmagnesium reagents with benzylic phosphates

A combination of copper chloride, triethyl phosphite, and tetrabutylammonium iodide is a very efficient catalytic system for the synthesis of polyfunctionalized diarylmethanes, using the cross-coupling reaction of arylmagnesium halides with benzylic phosphates. The antibiotic Trimethoprim has been prepared using this Cu(I)-catalyzed cross-coupling in 52% overall yield (four steps).

Dimethylzinc-Mediated, Enantioselective Synthesis of Propargylic Amines

A one-pot, enantioselective synthesis of N-aryl propargylic amines, using alkynylation reagents obtained from dimethylzinc and terminal acetylenes in combination with various aldehydes and o-methoxyaniline as starting materials, has been developed. Enantiopure beta-amino alcohols derived from norephedrine were used as non-covalent chiral auxiliaries, both in stoichiometric or substoichiometric amount. After optimization, propargylic amines were obtained in good to high yields (up to 93%) and with moderate to high enantiomeric excesses (up to 97% ee). The possibility to recover the chiral auxiliary after the reaction was demonstrated.

Suzuki-Miyaura cross-coupling reactions of benzyl halides with potassium aryltrifluoroborates

[reaction: see text] The palladium-catalyzed cross-coupling of potassium aryltrifluoroborates with benzylic halides occurs in good yield with high functional group tolerance. The increased stability of potassium aryltrifluoroborates compared to other boron coupling partners makes this an effective route to functionalized methylene-linked biaryl systems.

Copper-mediated cross-coupling of functionalized arylmagnesium reagents with functionalized alkyl and benzylic halides

[reaction: see text]. Functionalized arylmagnesium halides, prepared via an iodine-magnesium exchange, undergo a smooth cross-coupling reaction with functionalized primary alkyl iodides and benzylic bromides in the presence of CuCN.2LiCl, either in stoichiometric (with trimethyl phosphite as an additive) or catalytic quantities.