Enantioselective total synthesis of (-)-acylfulvene and (-)-irofulven

We report our full account of the enantioselective total synthesis of (-)-acylfulvene (1) and (-)-irofulven (2), which features metathesis reactions for the rapid assembly of the molecular framework of these antitumor agents. We discuss (1) the application of an Evans Cu-catalyzed aldol addition reaction using a strained cyclopropyl ketenethioacetal, (2) an efficient enyne ring-closing metathesis cascade reaction in a challenging setting, (3) the reagent IPNBSH for a late-stage reductive allylic transposition reaction, and (4) the final RCM/dehydrogenation sequence for the formation of (-)-acylfulvene (1) and (-)-irofulven (2).

The intermolecular Pauson-Khand reaction

Five membered carbocycles are important building blocks for many biologically active molecules. Moreover, substituted cyclopentenones (e.g. cyclopentenone prostaglandins) exhibit characteristic biological activity. The efficiency and atom economy of the Pauson-Khand reaction render this process potentially one of the most attractive methods for the synthesis of such compounds. Although it was discovered in its intermolecular form, the scope of the intermolecular Pauson-Khand reaction has always been limited by the poor reactivity and selectivity of the alkene component. The past decade, especially the last three years, has seen concerted efforts to broaden the scope of this reaction. In this overview, we provide a comprehensive and critical coverage of the intermolecular Pauson-Khand reaction based on the reactivity characteristics of different classes of alkenes and a rationalization of successes and misfortunes in this area.

Spiro-Cyclopropanation from Oxoallylsilanes

A novel highly stereoselective spiro-cyclopropanation reaction from oxoallylsilanes is described. Oxoallylsilanes are readily obtained by silylcupration of allene followed by conjugate addition to enones. The former oxoallylsilanes undergo a tandem cyclization-cyclopropanation reaction when treated with CH2I2/Me3Al, leading to hydroxylated polycyclic systems bearing the spiro-cyclopropane moiety. The scope of the process is studied, and a feasible pathway is discussed.

The Lewis acids catalyzed aza-Diels-Alder reaction of methylenecyclopropanes with imines

[reaction: see text] The methylenecyclopropanes can react with various imines to give the aza-Diels-Alder adducts in good yields in the presence of Lewis acids.