Halogenated Oxabicyclo[3.2.1]octadiene Building Blocks: Elaboration of the Dibromoenone

Abstract

We have been interested in exploiting the highly functionalized oxabicyclo[3.2.1]octadienes that are produced by the cycloaddition of furan and tetrabromocyclopropene as synthetic building blocks. As part of this program, we have prepared non-racemic derivatives of these adducts containing an α,β-dibromoenone moiety embedded in the bicyclic

Transition metals in organic synthesis: Highlights for the year 2005

“…Examples of ring systems include, bromooxabicyclo[3.2.1]octadiene [28], 5-trifloxyindoles [29], 6-halopurines [30] and 3,5-dichloro-2(H)-1,4-oxazin-2-one [31]. A palladium-catalyzed coupling of a 2-thiomethylbenzoxazole with a 2-pyridyltin reagent was used in a synthesis of pyridinyl boxazomycin C analogs [32].…”

“…(10) A large variety of functionalized heterocyclic halides and sulfonates were employed in the palladiumcatalyzed Suzuki reaction. Heterocyclic ring-systems such as, bromo-oxabicyclo[3.2.1]octadienes [28], 6-bromoimidazo[1,2-a]pyridine [174], 3,5-dichloropyrimidine and 3,5-dichloropyridine [175], 4,7-dibromo-2,1,3-benzothiazole with a 3-indolylboronic acid [176], halo-amino-pyridines, pyrazines and pyrimidines [154], chloropyrazines in a synthesis of botryllazines [14], 4-chloroquinoline-2-one [177], 3-trifloxypyrazole [178], 8-bromo-2 -deoxyguanosine [179], 2-chloro-2 -deoxyinosine [180], 6-halopurines [30], 6-fluoro-, 6-(3-methylbutylsulfanyl)-, and 6-(3-methylsulfonyl)purine [181], 5-trifloxyindoles [29], 3-iodo-5-bromoindole [182], 4-bromobenzofuran [183], 5,7-dichloro-1,6-naphthyridin-2-(1H)-one [184], 7-bromo-pyrido [2,3-b]pyrazine [185], 5-iodo-1,2,3-triazoles [186], 3-bromo-2,5-dihydrofuran-2-one [187], 3-halo-indazoles [188,189], 3-chloro-2-pyrazolines and 3-chloro-1-phenyl-1,4,5,6-tetrahydropyridazine [190] and 3-iodo-4H-chromen-4-one [191] were used in Suzuki type cross-couplings. Regioselective coupling in the 4-position of 3-bromo-4-trifloxyquinolin-2(1H)-one [192], the 2-position of di-and tribrominated pyrroles [193] and the 3-position of 3,5-dichloropyrazin-2-ones [194] were reported.…”

“…(14) Heterocyclic ring systems were shown to readily participate in Sonogashira-type couplings [175,306]. Some more complex examples include reaction of 5-iodoarabinosyluridine [307], 3-iodofuran [308], 6-chloro-9H-purine [309], 8-bromoadenosine [310], 2,6-bis(4-iodopyrazol-1-yl)pyridine [311], 6-chloro-3H-pyrimidin-4-one [312], bromo-oxabicyclo[3.2.1]octadienes [28], a triazolopyrazinyl bromide [172], 5-trifloxyindoles [29], 5-bromobenzofuran [183], 3-iodo-5-bromoindole and 3-iodo-5-bromo-3-indazole [182], 7-bromo-pyrido [2,3-b]pyrazine [185], 5-iodo-1,2,3-triazoles [186,313], 4,5-diiodoimidazole [314] and 4-iodo-2-bromoquinoline [315] derivatives. Sonogashira coupling of 2-iodophenols followed by cyclization to give benzofurans was reported [183].…”

The Frondosins: An Unusual Synthetic and Stereochemical Journey

“…[46][47][48][49] The S-furyl-alcohol could be prepared with excellent selectivity through reduction of ketone 56 with the (S,S)-Noyori transfer hydrogenation catalyst (Scheme 7). [50] After conversion into the corresponding silyl ether, 57 could be condensed with tetrabromocyclopropene (TBCP) to give a mixture of regioisomeric tetrabromides that, when directly treated with aqueous silver nitrate, produced regioisomeric enones 58 and 58b (58b not shown) in a 3.3:1 ratio.…”

The Cycloaddition Strategy for the Synthesis of Natural Products Containing Carbocyclic Seven‐Membered Rings

“…[24] The tetrabromoadduct can be converted into either isomer of the enantiomerically pure building blocks 60 through resolution of the corresponding tartrate ketals. [25] Elaboration of the unsubstituted olefin through a DielsAlder reaction [26] and the annulation of the dibromoenone through a chromium-mediated closure [27] has been used to generate the core structure of guanacastepene A. The tetrachloroadduct has been converted into the meso-diketone 61, which was elaborated to intermediate 63 through Robinson annulation chemistry.…”