Syntheses of highly substituted enantiopure C6 and C7 enones(1)

Total Synthesis of (-)-Mitrephorone A

The first synthesis of (-)-mitrephorone A is disclosed along with discussion and study of synthetic strategies. The natural product includes a highly congested hexacyclic ent-trachylobane diterpenoid framework featuring a rare, embedded oxetane. The synthetic analysis presented dissects a number of approaches for the synthesis of the central oxetane, including carbonyl-olefin photocycloadditions, Prins-type cyclizations, and oxidative ring closures. In the successful route, three [4 + 2] cycloadditions enable rapid construction of all carbocycles. A novel late-stage oxidative cyclization of a hydroxy diosphenol with Koser's reagent furnishes the pivotal oxetane moiety.

Palladium-Catalyzed Ullmann Cross-Coupling/Tandem Reductive Cyclization Route to Key Members of the Uleine Alkaloid Family

The trisubstituted cyclohexenone 12, generated through a palladium-catalyzed Ullmann cross-coupling reaction between o-iodonitrobenzene and a 4,5-trans-disubstituted 2-iodo-2-cyclohexen-1-one, engaged in a tandem reductive cyclization process upon exposure to hydrogen gas in the presence of Raney cobalt. As a result, the 1,5-methanoazocino[4,3-b]indole 13 was obtained and this could be readily elaborated to the racemic modifications of the alkaloids uleine, dasycarpidone, noruleine, and nordasycarpidone (1-4, respectively).

Exploiting amphiphilicity: facile metal free access to thianthrenes and related sulphur heterocycles

Benzodithioloimines are reacted with arynes or alkynes substituted with electron-withdrawing groups to afford the corresponding thianthrene or benzo[b][1,4]dithiine derivatives. The transformation takes place under mild reaction conditions without any transition metal. Furthermore, the reaction mode could be expanded to 2-thiocyanatopyrroles yielding pyrrolothiazoles.

Kinetic resolution of racemic 5-alkylcyclohexenones via Pd(ii)-catalyzed 1,4-additions of arylboronic acids – access to trans 3-alkyl-5-arylcyclohexanones

Ferrocenyl phosphapalladacycle catalyzed kinetic resolution of racemic 5-alkylcyclohexenones via arylboronic acid addition provides access to optically active trans-3-alkyl-5-aryl cycloalkanones.

Asymmetric approach toward chiral cyclohex-2-enones from anisoles via an enantioselective isomerization by a new chiral diamine catalyst

A 3-step asymmetric approach toward the optically active chiral cyclohex-2-enones from anisoles has been developed. The crucial asymmetric induction step is an unprecedented catalytic enantioselective isomerization of β,γ-unsaturated cyclohex-3-en-1-ones to the corresponding α,β-unsaturated chiral enones. This new asymmetric transformation was realized by cooperative iminium-base catalysis with an electronically tunable new organic catalyst. The synthetic utility of this methodology is highlighted by the enantioselective total synthesis of (-)-isoacanthodoral.

Enantioselective syntheses of candenatenins B and C using a chiral anthracene auxiliary

An asymmetric synthesis of two anticancer natural products, candenatenins B and C, is described, leading to a revision of the originally assigned stereochemistry. The synthesis follows a Diels-Alder/retro-Diels Alder strategy using a chiral anthracene auxiliary to access both targets with 90% ee. The inherent structural qualities of the auxiliary allow for both regio- and diastereoselective transformations.

Michael, Michael-aldol and Michael-Michael reactions of enolate equivalents of butane-2,3-diacetal protected glycolic acid derivatives

Consecutive coupling reactions of butane-2,3-diacetal protected glycolic acid derivatives with Michael acceptors and aldehydes are reported. An enantiopure sample of this building block was used to kinetically resolve a chiral Michael acceptor present as a racemic mixture of enantiomers.

Sulfur-Directed Synthesis of Enantiopure Hydroxy 2-Sulfinyl Butadienes

The treatment of sulfinyl chlorohydrins with KO-t-Bu in THF generates epoxy vinyl sulfoxides that undergo an efficient base-induced rearrangement to generate enantiopure hydroxy 2-sulfinyl dienes. This novel process takes place with high chemo- and stereoselectivity. The chirality at sulfur effectively controls the geometry of the trisubstituted alkene.

Synthesis of termini-differentiated 6-carbon stereotetrads: an alkylative oxidation strategy for preparation of the c21-c26 segment of apoptolidin(1)

[reaction: see text] Two methods have been developed for the synthesis of epoxide 36. The first uses (+)-pulegone 25 as an enantiopure starting material and introduces the requisite intricacy of target 22 in 12 operations. The second method employs an enantiospecific catalytic Jacobsen epoxidation of 1a and is five operations shorter. The second sequence features an oxygen-directed alkylative oxidation reaction that re-establishes the dienyl sulfone functionality with concomitant 1,3-transposition of the sulfone moiety.