Palladium mediated stereospecific synthesis of 3-enynyl substituted thioflavones/flavones

The stereocontrolled synthesis of enynes has been accomplished via a sequential Heck-Sonogashira reaction in a simple synthetic operation. A variety of terminal alkynes were reacted with 3-iodo(thio)flavone in the presence of a palladium catalyst and a copper salt affording a mild and one-pot method for the first synthesis of the corresponding 3-enynyl and/or alkynyl derivatives. The mechanism and scope of the reaction are discussed.     

Regio- and stereospecific synthesis of novel 3-enynyl-substituted thioflavones/flavones using a copper-free palladium-catalyzed reaction

[reaction: see text] A variety of 3-enynyl substituted flavones/thioflavones were synthesized via a sequential one-pot procedure using copper-free palladium-catalyzed cross coupling in a simple synthetic operation. The cross coupling between 3-iodo(thio)flavone and a broad range of terminal alkynes was carried out in the presence of Pd(PPh3)2Cl2 and triethylamine to afford the corresponding 3-enynyl derivatives in a regio- and stereoselective fashion. The best results are obtained by employing 3 equiv of the terminal alkynes. The process worked well irrespective of the substituents present on the (thio)flavone ring as well as in the terminal alkynes except arylalkynes. The reaction is quite regioselective, placing the substituent of the terminal alkyne at the far end of the double bond attached with the (thio)flavone ring. The orientation of the (thio)flavonyl and acetylenic moieties across the double bond was found to be syn in the products isolated. A tandem C-C bond-forming reaction in the presence of palladium catalyst rationalized the formation of coupled product. The catalytic process apparently involves heteroarylpalladium formation, regioselective addition to the C-C triple bond of the terminal alkyne, and subsequent displacement of palladium by another mole of alkyne. The present methodology is useful for the introduction of an enynyl moiety at the C-3 position of flavones and thioflavone rings to afford novel compounds of potential biological interest. In the presence of CuI the process afforded 3-alkynyl (thio)flavones in good yields.     

A new indolizidine synthesis

The intramolecular 1,6 Michael type addition of a primary amine to an electrophilic diene occurs under very mild conditions; it is the key step for a new preparation of indolizidines.     

A new tetrahydroisoquinoline synthesis

Cyclization of 2-vinylbenzylamines affords 1,2,3,4-tetrahydroisoquinolines. The synthesis of the vinylbenzylamines from benzhydrols or isoindolones is described.     

A new sulfene synthesis

Treatment of trimethylsilylmethanesulfonyl chloride with cesium fluoride in acetonitrile at room temperature has been found to produce sulfene which can be trapped in good yield.     

A new synthesis of phenylvinylselenides

Ketonic hydrazones react smoothly at room temperature in tetrahydrofuran in presence of an excess of $\text{t}$-butyltetramethylguanidine with phenylselenenyl bromide to give good to excellent yields of phenylvinylselenides.     

A new synthesis of pyrroles

The radical reaction between an N-ethylsulfonylenamide and an alpha-xanthyl ketone gives an intermediate gamma-keto imine which spontaneously ring-closes to the pyrrole.     

A new synthesis of tanikolide

We report a concise synthesis of tanikolide 1, which was obtained from ethyl 2-oxocyclopentanecarboxylate in four steps: alkylation, Baeyer-Villiger reaction, saponification, and reduction/lactonization, in 70% overall yield. Our strategy should be suitable for the preparation of 1 in multigram or larger quantities. The net result of the last two steps (i.e. saponification and reduction/lactonization) is an efficient reduction of the ethoxycarbonyl of 3 while keeping the lactone carbonyl intact.     

A new synthesis of oxazoles

Oxazoles are prepared from the ketoximes in a single pot sequence.     

A new synthesis of hydroxyphthalides

Cyclization of suitable enamino ketones can produce hydroxyphthalides.     

A new synthesis of pentafluorosulfanylbenzene

[reaction: see text] A new and convenient three-step synthesis of pentafluorosulfanylbenzene from 1,4-cyclohexadiene with an overall yield of >70% is reported along with a number of derivatization reactions.     

A new synthesis of brassicasterol

A new method has been developed for obtaining brassicasterol — the initial compound for the synthesis of the natural brassinosteroid epibrassinolide.Institute of Bioorganic Chemistry, Belorussian Academy of Sciences, Minsk. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 90–93, January–February, 1992.     

A new synthesis of methanoisoindoles

Russian Journal of Organic Chemistry -