Synthesis of oxa-bridged derivatives from Diels-Alder bis-adducts of butadiene and 1,2,3,4-tetrahalo-5,5-dimethoxycyclopentadiene.

Bis-adducts of 1,2,3,4-tetrahalo-5,5-dimethoxycyclopentadiene and 1,3-butadiene, generated in situ from 3-sulfolene, have been synthesized in excellent yield. Ruthenium catalyzed oxidation of the bis-adducts followed by a one-pot transformation of the resulting alpha-diketone furnished oxa-bridged compounds. Unambiguous stereochemical assignments of both diastereomeric series are reported.

Azacrown-oxabridged macrocycle: a novel hybrid fluorogenic chemosensor for transition and heavy metal ions.

A novel hybrid of azacrown ether-oxabridged fluorogenic chemosensor (1) has been synthesized: the metal ion binding ability of the hybrid molecule shows higher affinity towards transition metal ion Zn(2+) and heavy metal ion Hg(2+) compared to the parent azacrown ether which shows poor metal ion selectivity: the binding modes of the Zn(2+) and Na(+) towards have been discussed.

Serendipitously discovered diazomethane-mediated novel molecular rearrangements of norbornyl alpha-ketohemiketals.

[reaction: see text] Unprecedented molecular rearrangements during diazomethane-mediated reaction of norbornyl alpha-ketohemiketals leading to novel molecular entities are presented. A dramatic change in the reaction outcome was noted for five- and six-membered alpha-ketohemiketals: the former predominantly furnished rearranged bicyclic products involving migration of the gamma-alkoxy group, and the latter furnished the oxetane derivative as the major product. Interestingly, six-membered O-methyl-ketal yielded a product arising from the migration of the vicinal alkoxy group.

Concise synthesis of novel oxa-bridged compounds.

[structures: see text] A stereoselective strategy for the replacement of the 1,2-dihaloalkene bridge of tetrahalonorbornyl derivatives by an oxygen bridge involving stepwise controlled oxidation, cleavage of the dione thus formed, and reiterative intramolecular S(N)2 displacement of two bridgehead halogens is devised. The synthesis of four highly strained pentacyclic bis-oxa-bridged derivatives 10, 27, 28, and 29 with interesting structural variations is presented. The two oxa bridges are syn to each other, separated by central cyclohexane and cycloheptane rings in 10 and 27, while they are anti to each other and are separated by central cyclopentane and furan rings in 28 and 29. In the case of the highly symmetric bis-oxa-bridged derivative 10 the two syn oxa bridges constrain the central cyclohexane ring into the boat form. The endo,anti,endo 2:1 bis adducts of 1,2,3,4-tetrahalo-5,5-dimethoxycyclopenta-1,3-diene with cyclopentadiene were prepared for the first time, while the reactivites of previously unexplored bis adducts derived from furan and cycloheptatriene were revealed.

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.

Aluminum chloride-induced heteroarylation of arenes and heteroarenes. 2. A new synthesis of 4-substituted phthalazin-1(2H)-ones.

We herein report the efficient syntheses of 4-(hetero)aryl-substituted 1-chlorophthalazines via heteroarylation of arenes/heteroarenes through AlCl(3)-induced C[bond]C formation reactions. A number of (hetero)arenes were reacted with 1,4-dichlorophthalazine to give aryl/heteroaryl-substituted phthalazines in good to excellent yields. Many of them were converted to the corresponding phthalazin-1(2H)-ones.

Palladium-catalyzed cleavage of O/N-propargyl protecting groups in aqueous media under a copper-free condition.

[reaction: see text] A copper-free palladium-mediated cleavage of O/N-propargyl bonds in aqueous media has been investigated, affording a mild and convenient method for the deprotection of phenols and anilines. The methodology could be utilized for the selective removal of propargyl groups from aryl ethers and amines without affecting a variety of unprotected functional groups present in the substrates. The mechanism and scope of the reaction is discussed.