Palladium-Catalyzed Asymmetric Hydrophosphination of Internal Alkynes: Highly Regio- and Stereoselective Construction of Axially Chiral Phosphines

Palladium-catalyzed unprecedented atroposelective hydrophosphination of internal alkynes has been realized using diarylphosphines, affording C-N axially chiral trisubstituted olefins (vinylphosphines) in excellent regioselectiviry, (E)-selectivity, and enantioselectivity. The axial chirality was established via integration of hydrophosphination and dynamic kinetic transformation of the alkynes, with both symmetrical and nonsymmetrical secondary phosphines being applicable. In the latter case, additional P-central chirality has been constructed in good diastereoselectivity.

Direct Synthesis of Enones by Visible-Light-Promoted Oxygenation of Trisubstituted Olefins Using Molecular Oxygen

A one-step synthesis of enones from olefins is described. The reaction was performed under visible-light irradiation in the presence of molecular oxygen and a photocatalyst. The reaction proceeded with various types of trisubstituted olefins to give enones in good yields with high regioselectivity. In particular, oxygen- and nitrogen-containing functional groups, heteroaromatic rings, and cyclopropanes were tolerated. Mechanistic studies and previous reports indicated that the active oxygen species generated in the reaction system is singlet oxygen.

Diastereoselective synthesis of trisubstituted olefins using a silicon-tether ring-closing metathesis strategy

We report an efficient and diastereoselective synthesis of E- and Z-trisubstituted alkenes by a silicon-tether ring-closing metathesis strategy.

A Relay Strategy Actuates Pre-Existing Trisubstituted Olefins in Monoterpenoids to Form New Trisubstituted Olefins by Cross Metathesis

<b><u>Abstract:</u></b> A retrosynthetic disconnection-reconnection analysis of epoxypolyenes – substrates that can undergo cyclization to podocarpane-type tricycles – reveals relay-actuated Δ^6,7-functionalized monoterpenoid alcohols for ruthenium benzylidene catalyzed olefin cross metathesis with homoprenyl benzenes. Successful implementation of this approach provided several epoxypolyenes as expected (<i>E</i>:<i>Z</i>, ca. 2-3:1). The method is further generalized for the cross metathesis of pre-existing trisubstituted olefins in other relay-actuated Δ^6,7-functionalized monoterpenoid alcohols with various other trisubstituted alkenes to form new trisubstituted olefins. Epoxypolyene cyclization of an enantiomerically pure, but geometrically impure, epoxypolyene substrate provides an enantiomerically pure, trans-fused, podocarpane-type tricycle (from the <i>E</i>-geometrical isomer).<br>

A Relay Strategy Actuates Pre-Existing Trisubstituted Olefins in Monoterpenoids to Form New Trisubstituted Olefins by Cross Metathesis

<b><u>Abstract:</u></b> A retrosynthetic disconnection-reconnection analysis of epoxypolyenes – substrates that can undergo cyclization to podocarpane-type tricycles – reveals relay-actuated Δ^6,7-functionalized monoterpenoid alcohols for ruthenium benzylidene catalyzed olefin cross metathesis with homoprenyl benzenes. Successful implementation of this approach provided several epoxypolyenes as expected (<i>E</i>:<i>Z</i>, ca. 2-3:1). The method is further generalized for the cross metathesis of pre-existing trisubstituted olefins in other relay-actuated Δ^6,7-functionalized monoterpenoid alcohols with various other trisubstituted alkenes to form new trisubstituted olefins. Epoxypolyene cyclization of an enantiomerically pure, but geometrically impure, epoxypolyene substrate provides an enantiomerically pure, trans-fused, podocarpane-type tricycle (from the <i>E</i>-geometrical isomer).<br>

Relay Cross Metathesis for the Iterative Ascent of the Terpenoids

<div>We report the design and implementation of a relay cross</div><div>metathesis (ReXM) reaction for the ascent of the terpenoids in an iterative protocol. The method features the reaction of naturally occurring terpenoid building blocks – with preexisting trisubstituted olefins – which combine to construct a new trisubstituted olefin resulting in a five-carbon unit homologation. Subsequent functional group manipulation allows for the method to be repeated in an</div><div>iterative fashion. The method is used for the synthesis of a diterpenebenzoate macrolide of biogenetic relevance to the bromophycolide family of natural products.</div>