Cycloisomerization of 1,n-Enynes: Challenging Metal-Catalyzed Rearrangements and Mechanistic Insights

Highly enantioselective construction of axial chirality by palladium-catalyzed cycloisomerization of N-alkenyl arylethynylamides

A cationic palladium(II)/(S)-xyl-Segphos complex catalyzes enantioselective cycloisomerizations of N-alkenyl arylethynylamides leading to axially chiral 4-aryl-2-pyridones in high yields with high ee values. The present catalysis represents the first enantioselective construction of axial chirality by the transition-metal-catalyzed cycloisomerization.

Computational Studies on the Pt(II)-Catalyzed Cycloisomerization of 1,6-dienes into Bicyclopropanes: A Mechanistic Quandary Evaluated by DFT

The mechanism of the (bis(phosphanylethyl)phosphane)Pt(2+) catalyzed cyclo-isomerization reaction of 7-methyl-octa-1,6-diene to form 1-isopropylbicyclo[3.1.0]hexane was studied using computational methods. The cyclopropanation step was found to be the turnover-limiting step. The overall reaction proceeds via both a 5-exo and a 6-endo route. W conformations were shown to facilitate cyclopropanation, but do not have any influence on the rate of the 1,2-hydride shifts.

Ruthenium- and palladium-catalyzed enyne cycloisomerizations: differentially stereoselective syntheses of bicyclic structures

Enyne cycloisomerizations can provide an efficient means for forming carbon-carbon bonds. We describe stereoselectively dichotomous enyne cycloisomerizations, entirely dependent on the selection of catalytic manifold. Ruthenium catalysis provides trans-fused bicyclic systems, whereas palladium catalysis provides the analogous cis-fused bicycles. A number of substrates are investigated, and the outcomes ultimately offer a clear mechanistic rationale for these observations.

Au(I)-Catalyzed cycloisomerizations terminated by sp(3) C-H bond insertion

The gold(I)-catalyzed cycloisomerization of 1,5-enynes and 1,4-allylallenes to tetracyclododecane and tetracyclotridecane derivatives, respectively, is reported. Complexation of the cationic gold(I) complex to either the alkyne or allene moiety induces an intramolecular addition of the alkene, leading to a gold(I)-stabilized carbenoid intermediate. This intermediate undergoes a formal sp(3) C-H insertion to generate the tetracyclic adduct. A series of deuterium labeling experiments showed that the C-H functionalization step proceeds with an inverse kinetic isotope effect.

Platinum(II) Enyne Cycloisomerization Catalysis: Intermediates and Resting States

In situ generated [(PPP)Pt][BF(4)](2) (PPP = triphos) catalyzes the cycloisomerization of 1,6-enyne-ols by initiative pi-activation of the alkyne. This generates an isolable cationic Pt-alkenyl species which subsequently participates in turnover limiting protonolysis with in situ generated acid. This latter reactivity contrasts cationic Pt-alkyls which are more difficult to protonolyze. Mechanistic studies on isolated Pt-alkenyls, and deuterium labeling helped to elucidate the mechanistic details.

Iron-mediated intramolecular metalative cyclization of alpha,beta-unsaturated esters and amides. Versatile one-pot preparation of bicyclic ketoesters

2-Nonen-7-ynedioic or 2-decen-8-ynedioic acid derivatives were treated with an iron reagent generated from FeCl2 and t-BuMgCl in a ratio of 1:4 to give cyclized products after hydrolysis, deuteriolysis, or the addition of carbonyl compounds. Upon reaction with the same iron reagent, 2,7-nonadienedioates afforded bicyclic ketoesters (and their enol forms) after the addition of s-BuOH or carbonyl compounds.

Au(I)-catalyzed ring expanding cycloisomerizations: total synthesis of ventricosene

The gold(I)-catalyzed cycloisomerization of enynes containing an embedded cyclopropane unit leads selectively to the formation of ring systems containing the cyclopropylmethyl cation. A subsequent Wagner-Merwein shift provides diastereomerically pure fused cyclobutanes. The utility of this methodology for the rapid assembly of polycyclic ring systems is illustrated by the total synthesis of the angular triquinane ventricosene.