Geminal Alkene–Alkyne Cross Metathesis Using a Relay Strategy

Abstract

A relay strategy was employed to achieve an intermolecular ene-yne metathesis between 1,1-disubstituted alkenes and alkynes. The relay serves to activate an unreactive alkene which will not participate in ene-yne metathesis. The new relay cross ene-yne metathesis gives rise to 1,1,3-trisubstituted-1,3-dienes previously inaccessible by direct ene-yne metathesis methods.

A Relay Strategy Actuates Pre-Existing Trisubstituted Olefins in Monoterpenoids for Cross-Metathesis with Trisubstituted Alkenes

“…A possible catalytic cycle for this ReXM process using representative epoxide ( E )- 5a with homoprenyl benzene 7a invokes Diver for the conversion of A to B with loss of dihydrofuran (Figure ). The regioselective reactions of ruthenium species of type B with trisubstituted olefins have been proposed by Robinson, which would produce the ReXM product 8a and ruthenium isopropylidene C .…”

“…Herein, we report the success of this unprecedented olefin–olefin combination to form new unfunctionalized trisubstituted olefins by cross-metathesis (Figure e), where the overall transformation can be classified as a relay cross-metathesis. This relay cross-metathesis reaction (“ReXM”) distinguishes itself from the very limited literature precedent for such reactions by being the first such example to form isolated, unconjugated, trisubstituted alkenes where all previous reports have formed conjugated alkenes. , …”

Tandem cross enyne metathesis (CEYM)–intramolecular Diels–Alder reaction (IMDAR). An easy entry to linear bicyclic scaffolds

“…The use of Lewis acids as co-catalysts was also tested although the efficiency of the process did not improve neither with Ti(OiPr) 4 nor with BF 3 ·OEt 2 ( Table 1 , entries 11 and 12). Alternatively, thiourea derivatives have proven to be very effective hydrogen-bonding catalysts for Diels–Alder reactions [ 28 ]. However, in our case no influence was observed when the reaction was performed in the presence of diaryl thioureas ( Table 1 , entry 13).…”

Bifunctional Ligand Enables Efficient Gold‐Catalyzed Hydroalkenylation of Propargylic Alcohol

“…The dienol motif of 3 can be found as key structural components of either natural products or in key intermediates in natural product synthesis and, because of its densely packed functionalities, is rich with reactivity . As summarized in Scheme b, it can be mainly assembled in the following manners, but with limitations: i) the Suzuki–Miyaura coupling, which is straightforward but requires difficult‐to‐access chiral α‐haloallylic alcohols to prepare chiral 3 ; ii) the addition of buta‐2,3‐dien‐1‐ylmetal species to aldehydes, which are mostly explored without substitution (i.e., R=H) or lead selectively to the formation of products possessing a Z ‐configured double bond distal to the hydroxy group when R≠H, and hence display limited product scope; iii) transition metal catalyzed hydroalkenylations–, of propargylic alcohols using boronic acids, and the reported examples employ only internal propargyl alcohol substrates– and exhibit either the opposite or poor regiochemistry; iv) intermolecular enyne metathesis, which displays low/moderate E / Z selectivities; v) one related case of an oxidative Heck reaction (57 % yield; not shown) …”