Stereoselectivity of electrophile-promoted oxacyclizations of 1,4-dihydroxy-5-alkenes to 3-hydroxytetrahydropyrans

Advances in mercury(II)-salt-mediated cyclization reactions of unsaturated bonds

The synthesis of complex cyclic compounds is extremely challenging for organic chemists. Many transition-metal-salt-mediated cyclizations are reported in literature. Hg(II) salts have been successfully employed in cyclizations to form complex heterocyclic and carbocyclic structures that are impossible to synthesize with other transition metal salts. In this review, we have summarized cyclization reactions that are performed with Hg(II) salts. These salts are also successfully applied in stoichiometric or catalytic amounts to form complex cyclic structures and natural products.

Tethered Silanoxymercuration of Allylic Alcohols

We present the first examples of tethered olefin functionalization reactions using a silanol auxiliary. A range of allylic alcohols are readily condensed with di-tert-butylsilyl bis(trifluoromethanesulfonate) to form allylic silanols. When treated with Hg(OTf)₂ and NaHCO₃, these silanols easily transform into cyclic silanediol organomercurial compounds. In most cases, the reactions are exquisitely diastereoselective. The scale can be increased more than 10-fold without a loss of yield and selectivity. We demonstrate that the silanediols are versatile synthons for a variety of further reactions.

Sequential exo-mode oxacyclizations for the synthesis of the CD substructure of brevenal

We describe a novel strategy for synthesizing the CD bicyclic ether substructure of the fused polycyclic ether natural product brevenal. This product arises from a three-step sequence beginning with (1) regio- and diastereoselective iodoetherification of an acyclic diene-diol, followed by (2) alkene metathesis with an epoxyalkene synthon, concluding with (3) palladium-catalyzed cycloisomerization. Despite the modest yield and long reaction period for the cycloisomerization step, these studies provide valuable insights into the nature of byproducts generated and the mechanisms by which they form. This work demonstrates a portion of a larger synthetic strategy for constructing the pentacyclic core of brevenal from an acyclic precursor.

Modular synthesis of allyl vinyl ethers for the enantioselective construction of functionalized quaternary stereocenters

A flexible synthesis of allyl vinyl ethers, precursors of functionalized quaternary stereocenters, was developed by employing a regioselective Petasis olefination of haloallyl oxalates and subsequent cross-coupling with alkyl- and aryl boronic acids.

Gold-catalyzed spiro-N,O-ketal synthesis

An efficient method for the synthesis of spiro-N,O-ketals with 5- and 6-membered rings was developed via a gold-catalyzed spiroamidoketalization of alkynyl amidoalcohols under mild conditions.