Regioselective Cross-Coupling Reactions Research Articles

Some regioselective cross-coupling reactions of halopyridines and halopyrimidines

An efficient procedure for cross-coupling of 3-bromopyridine and 4-bromoanisole to various mono- and dichloro heteroaryl compounds—giving the corresponding biaryls in 74–96% yield—is described.

Synthesis of 2'-substituted 4-bromo-2,4'-bithiazoles by regioselective cross-coupling reactions.

The synthesis of the title compounds (1) was achieved in two steps starting from readily available 2,4-dibromothiazole (2). In a regioselective Pd(0)-catalyzed cross-coupling step, compound 2 was converted into a variety of 2-substituted 4-bromothiazoles 3 (10 examples, 65-85% yield). Alkyl and aryl zinc halides were employed as nucleophiles to introduce an alkyl or aryl substituent. The Sonogashira protocol was followed to achieve an alkynyl-debromination. Bromo-lithium exchange at carbon atom C-4 and subsequent transmetalation to zinc or tin converted the 4-bromothiazoles 3 into carbon nucleophiles which underwent a second regioselective cross-coupling with another equivalent of 2,4-dibromothiazole (2). The Negishi cross-coupling gave high yields of the 2'-alkyl-4-bromo-2,4'-bithiazoles 1a-g (88-97%). The synthesis of the 2'-phenyl- and 2'-alkynyl-4-bromo-2,4'-bithiazoles 1h-j required a Stille cross-coupling that did not proceed as smoothly as the Negishi cross-coupling (58-62% yield). The title compounds which were accessible in total yields of 38-82% are versatile building blocks for the synthesis of 2,4'-bithiazoles.

Regioselective Cross-Coupling Reactions as an Entry into Biologically Relevant Bithiazoles: First Total Synthesis of Cystothiazole E.

No problems have been encountered while using bithiazoles in Pd-catalyzed cross-coupling reactions. It was thus possible to achieve the first synthesis of cystothiazole E (1) with a Suzuki coupling of the building blocks 2 and 3 as the pivotal C-C bond-formation step (94 % yield, TBDMS=tBuMe2 Si). The bithiazole 3 could be prepared very conveniently from 2,4-dibromothiazole by regioselective cross-coupling reactions.

Synthesis of 4-alkyl-3-bromo-2(5 H)-furanones and unsymmetrically disubstituted 3,4-dialkyl-2(5 H)-furanones by palladium-catalyzed cross-coupling reactions

Easily available 3,4-dibromo-2( 5H)-furanone undergoes a regioselective cross-coupling reaction with alkylboronic acids in the presence of catalytic amounts of PdCl 2(MeCN) 2 and AsPh 3 and a large molar excess of Ag 2O to provide the corresponding 4-alkyl-3-bromo-2(5 H)-furanones in satisfactory yields. These monobromo derivatives have proven to be useful precursors to unsymmetrically substituted 3,4-dialkyl-2(5 H)-furanones which include the racemic form of naturally occurring seiridin.

Bis(2,2,2-trifluoroethyl)phosphate as a Leaving Group for Highly Regioselective Cross-Coupling Reactions of Allylic Alcohol Derivatives with Allylic Organometallics

Regioselective cross-coupling reaction of allylic alcohol derivatives with allylic metal reagents were achieved using bis(2,2,2-trifluoroethyl)phosphate as a leaving group. Reaction with allylic magnesium reagent resulted in α,γ’ cross-coupling, whereas α,α’ cross-coupling occurred with allylic barium reagent. When a 1:1 mixture of (E)-2-octenyl 1-bis(2,2,2-trifluoroethyl)phosphate and (E)-2-decenyl chloride was treated with 1 equiv of reactive barium, the cross-coupling products were obtained with 86% selectivity and an α,α’/α,γ’ ratio of 94/6.

ChemInform Abstract: Regioselective Cross‐Coupling Reaction of Phenylthioethynyl Magnesium Bromide with Allylic Halides: Synthesis of Skipped Phenylthiopentenynes.

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