PBu3-Mediated Vinylogous Wittig Reaction of α-Methyl Allenoates with Aldehydes and Mechanistic Investigations

A bicyclization reaction with two molecular allenyl ketones and isocyanides: synthesis of a lactone-containing azaspirocycle derivative

A novel bicyclization reaction of two molecular allenyl ketones and isocyanides has been disclosed. This strategy allows for the construction of structurally complex spirocyclic lactam–lactone systems in an efficient manner.

Phosphine-mediated sequential annulations of allenyl ketone and isocyanide: a bicyclization strategy to access a furan-fused eight-membered ring and a spirocycle

Phosphine-mediated cascade annulations of allenyl ketone and isocyanide have been disclosed. This strategy enables the efficient synthesis of a furan-fused eight-membered ring and a spirocycle.

Carbon-nitrogen bond cleavage of pyridine with two molecular substituted allenoates: access to 2-arylpyrimidin-4(3H)-one

A DABCO-catalyzed annulation reaction of pyridin-2-amine and substituted allenoates has been disclosed. This strategy allows for the ring-opening of a pyridine ring system and the formation of two new rings including a pyrimidinone ring and a benzene ring in an efficient manner.

Phosphine Organocatalysis

The hallmark of nucleophilic phosphine catalysis is the initial nucleophilic addition of a phosphine to an electrophilic starting material, producing a reactive zwitterionic intermediate, generally under mild conditions. In this Review, we classify nucleophilic phosphine catalysis reactions in terms of their electrophilic components. In the majority of cases, these electrophiles possess carbon-carbon multiple bonds: alkenes (section 2), allenes (section 3), alkynes (section 4), and Morita-Baylis-Hillman (MBH) alcohol derivatives (MBHADs; section 5). Within each of these sections, the reactions are compiled based on the nature of the second starting material-nucleophiles, dinucleophiles, electrophiles, and electrophile-nucleophiles. Nucleophilic phosphine catalysis reactions that occur via the initial addition to starting materials that do not possess carbon-carbon multiple bonds are collated in section 6. Although not catalytic in the phosphine, the formation of ylides through the nucleophilic addition of phosphines to carbon-carbon multiple bond-containing compounds is intimately related to the catalysis and is discussed in section 7. Finally, section 8 compiles miscellaneous topics, including annulations of the Hüisgen zwitterion, phosphine-mediated reductions, iminophosphorane organocatalysis, and catalytic variants of classical phosphine oxide-generating reactions.

Bridged [2.2.1] bicyclic phosphine oxide facilitates catalytic γ-umpolung addition-Wittig olefination

A novel bridged [2.2.1] bicyclic phosphine oxide, devised to circumvent the waste generation and burdens of purification that are typical of reactions driven by the generation of phosphine oxides, has been prepared in three steps from commercially available cyclopent-3-ene-1-carboxylic acid. The performance of this novel phosphine oxide was superior to those of current best-in-class counterparts, as verified experimentally through kinetic analysis of its silane-mediated reduction. It has been applied successfully in halide-/base-free catalytic γ-umpolung addition-Wittig olefinations of allenoates and 2-amidobenzaldehydes to produce 1,2-dihydroquinolines with good efficiency. One of the 1,2-dihydroquinoline products was converted to known antitubercular furanoquinolines.

Phosphine-catalysed α-umpolung addition of nucleophiles to δ-acetoxy allenoates: stereoselective synthesis of 2,4-dienoates

The first example of phosphine-catalyzed α-umpolung addition of nucleophiles to allenoates is described, which features the use of δ-acetoxy allenoate to generate a 3-phosphonium-2,4-dienoate intermediate, thus facilitating the α-umpolung addition of nucleophiles.

Phosphine-Mediated Iterative Arene Homologation Using Allenes

A PPh3-mediated multicomponent reaction between o-phthalaldehydes, nucleophiles, and monosubstituted allenes furnishes functionalized non-C2-symmetric naphthalenes in synthetically useful yields. When the o-phthalaldehydes were reacted with 1,3-disubstituted allenes in the presence of PPh2Et, naphthalene derivatives were also obtained in up to quantitative yields. The mechanism of the latter transformation is straightforward: aldol addition followed by Wittig olefination and dehydration. The mechanism of the former is a tandem γ-umpolung/aldol/Wittig/dehydration process, as established by preparation of putative reaction intermediates and mass spectrometric analysis. This transformation can be applied iteratively to prepare anthracenes and tetracenes using carboxylic acids as pronucleophiles.

Double γ-alkylation of allylic phosphorus ylides: a unique access to oxa-bicyclic[3.3.0] diene skeletons

A new ylide-initiated tandem cyclization reaction based on γ-dialkylation of allylic ylides has been realized, delivering a series of [3.3.0] oxa-bicyclic dienes in high yields with perfect diastereoselectivity.

Convenient synthesis of substituted tetrahydrofuran via Lewis base catalyzed [3 + 2] domino reactions

A DABCO catalyzed domino reaction between 3-oxo-4-(2-oxoindolin-3-ylidene) butanoates and allenoates furnished 2,3,5-substituted tetrahydrofuran furan derivatives bearing oxindole moiety and two exocyclic double bonds in high yield.

Recent advances in stereoselective synthesis of 1,3-dienes

The aim of this review is to present the latest developments in the stereoselective synthesis of conjugated dienes, covering the period 2005-2010. Since the use of this class of compounds is linked to the nature of their appendages (aryls, alkyls, electron-withdrawing, and heterosubstituted groups), the review has been categorized accordingly and illustrates the most representative strategies and mechanisms to access these targets.