Titanium(IV) bromide and boron(III) tribromide promoted reactions of arylaldehydes with 3-butyn-2-one, methyl propiolate and propynenitrile

The reaction of porphyrins with α,β-acetylenic ketone/ester (Morita-Baylis-Hillman) promoted by MgI2 and subsequent Sonogashira coupling reactions

The stereoselective synthesis of (Z)-β-iodovinyl ketones/esters of Morita-Baylis-Hillman (MBH) porphyrin adducts has been achieved with a tandem formation of C - C and C - I bonds in a three-component reaction. The reaction is promoted by MgI 2 as a Lewis acid, as well as an iodine source for a Michael-type addition. The MBH adducts are efficiently oxidized to the corresponding ketones with Dess-Martin periodinane (DMP). These scaffolds are further used in a palladium-catalyzed Sonogashira carbon-carbon coupling reaction to obtain highly extended porphyrin systems.

Allylic and allenic halide synthesis via NbCl(5)- and NbBr(5)-mediated alkoxide rearrangements

Addition of NbCl(5) or NbBr(5) to a series of magnesium, lithium, or potassium allylic or propargylic alkoxides directly provides allylic or allenic halides. Halogenation formally occurs through a metalla-halo-[3,3] rearrangement, although concerted, ionic, and direct displacement mechanisms appear to operate competitively. Transposition of the olefin is equally effective for allylic alkoxides prepared by nucleophilic addition, deprotonation, or reduction. Experimentally, the niobium pentahalide halogenations are rapid, afford essentially pure (E)-allylic or -allenic halides after extraction, and are applicable to a range of aliphatic and aromatic alcohols, aldehydes, and ketones.