Transition-Metal Radical Source Research Articles

ChemInform Abstract: Total Synthesis of (.+-.)-Dihydroprotolichesterinic Acid and Formal Synthesis of (.+-.)-Roccellaric Acid by Radical Cyclization of an Epoxide Using a Transition-Metal Radical Source.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Stereoselective Synthesis of Polysubstituted Tetrahydropyrans by Radical Cyclization of Epoxides Using a Transition-Metal Radical Source.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Short and stereoselective total synthesis of furano lignans (+/-)-dihydrosesamin, (+/-)-lariciresinol dimethyl ether, (+/-)-acuminatin methyl ether, (+/-)-sanshodiol methyl ether, (+/-)-lariciresinol, (+/-)-acuminatin, and (+/-)-lariciresinol monomethyl ether and furofuran lignans (+/-)-sesamin, (+/-)-eudesmin, (+/-)-piperitol methyl ether, (+/-)-pinoresinol, (+/-)-piperitol, and (+/-)-pinoresinol monomethyl ether by radical cyclization of epoxides using a transition-metal radical source.

Intramolecular radical cyclization of suitably substituted epoxy ethers 4a-g using bis(cyclopentadienyl)titanium(III) chloride as the radical source resulted in trisubstituted tetrahydrofurano lignans and 2,6-diaryl-3,7-dioxabicyclo[3.3.0]octane lignans depending on the reaction conditions. The titanium(III) species was prepared in situ from commercially available titanocene dichloride and activated zinc dust in THF. Upon radical cyclization followed by acidic workup, epoxy olefinic ethers 4a-g afforded furano lignans dihydrosesamin 1a, lariciresinol dimethyl ether 1b, acuminatin methyl ether 1e, and sanshodiol methyl ether 1g directly and lariciresinol 1h, acuminatin 1i, and lariciresinol monomethyl ether 1j after removal of the benzyl protecting group by controlled hydrogenolysis of the corresponding cyclized products. The furofuran lignans sesamin 2a, eudesmin 2b, and piperitol methyl ether 2e were also prepared directly by using the same precursors 4a-f on radical cyclization followed by treatment with iodine and pinoresinol 2h, piperitol 2i, and pinoresinol monomethyl ether 2j after controlled hydrogenolysis of the benzyl protecting group of the corresponding cyclized products. Two naturally occurring acyclic lignans, secoisolariciresinol 5h and secoisolariciresinol dimethyl ether 5b, have also been prepared by exhaustive hydrogenolysis of 2h and 2b, respectively.

Short and Stereoselective Total Synthesis of (±)-Dihydrosesamin and (±)-Acuminatin Methyl Ether by Radical Cyclisation of Epoxides Using a Transition-Metal Radical Source

Short and Stereoselective Total Synthesis of (±)-Dihydrosesamin and (±)-Acuminatin Methyl Ether by Radical Cyclisation of Epoxides Using a Transition-Metal Radical Source

A short and stereoselective total synthesis of (±)-sesamin by radical cyclisation of an epoxide using a transition-metal radical source

A short, efficient and stereoselective synthesis of a furofuran lignan, (±)-sesamin, has been achieved in good overall yield through the radical cyclisation of an epoxide using a Ti(III) reagent as the radical initiator.

Total synthesis of (±)-Dihydroprotolichesterinic acid and Formal synthesis of (±)-Roccellaric acid by radical cyclisation of an epoxide. Using a transition-metal radical source

A short and efficient total synthesis of (±)-Dihydroprotolichesterinic acid ( 1) and Formal synthesis of (±)-Roccellaric acid ( 2) has been acheived by radical cyclisation of epoxide using a transition metal radical source.

Stereoselective Synthesis of Polysubstituted Tetrahydrofurans by Radical Cyclization of Epoxides Using a Transition-Metal Radical Source. Application to the Total Synthesis of (±)-Methylenolactocin and (±)-Protolichesterinic Acid

Radical cyclization reactions of substituted α-(prop-2-ynyloxy) epoxides using bis(cyclopentadienyl)titanium(III) chloride as the radical source resulted in polysubstituted tetrahydrofurans. Titanium(III) species were prepared in situ from commercially available titanocene dichloride and zinc dust in tetrahydrofuran. Upon radical cyclization, 2-aryl epoxides 3a−e afforded only trans products 4a−e whereas the 2-alkyl epoxides 3f−h formed a mixture of isomeric products 4f−h in a ratio of 5:1. Some of the aryl tetrahydrofuran derivatives have already been used for the synthesis of bioactive furofuran lignans. 2-Pentyl-3-(hydroxymethyl)-4-methylenetetrahydrofuran (4f) and 2-tridecyl-3-(hydroxymethyl)-4-methylenetetrahydrofuran (4g) have been transformed to two antitumor antibiotics (±)-methylenolactocin (1f) and (±)-protolichesterinic acid (1g), respectively, in good overall yield.