The first synthesis of raputimonoindole A from the tree Raputia praetermissa (Rutaceae) is reported, starting from indole‐5‐carbaldehyde. The key step is Braun′s diastereoselective Heck–Suzuki cascade that assembled the prenylated methylenetetrahydrofuran moiety. The unsubstituted indole enamine functionality was tolerated, and the absolute configuration of naturally occurring raputimonoindole A is assigned as (R,R). Raputimonoindole B was accessed by Ir‐catalyzed C–H activation/borylation followed by Suzuki–Miyaura cross‐coupling. Two biosynthetically related 5‐(dihydrofuran‐2‐yl)indole derivatives from R. simulans were synthesized by ring‐closing metathesis, and their absolute configurations were determined.
The photoreactivity of a series of hitherto unknown, multiply fluorinated 2-azidobenzimidazole derivatives was investigated. The synthesis of the starting material includes regioselective pdefluorination of nitrobenzene derivatives employing Ogoshi's conditions. If the 6-position was unsubstituted, irradiation in the presence of N-protected amino acids at 300 nm (Rayonet) led to the formation of arylesters by oxygenation of the 6position in good to excellent yields and perfect regioselectivity. We did not observe any displacement of fluoride. If the 6position itself was fluorinated, alternative positions of the benzene portion were attacked. Mechanistically, the reaction proceeds through ring opening of the singlet nitrene to the cyanodiimine or via the iminobenzimidazolium ion. The availability of a set of fluorinated photo-adducts prompted the quantum chemical calculation of their 19 F NMR chemical shifts. Even with the most suitable method investigated (ωB97XD/ TApr-cc-pVDZ), deviations of up to 5 ppm from the experimental values were observed, underlining the importance of experimental measurements.
The marine natural
product ageladine A was synthesized by exploiting
novel aza-BODIPY-type boron complexes that allowed the regioselective
dibromination of the pyrrole unit, as confirmed by quantum chemical
calculation (ωB97XD/TApr-cc-pVDZ). The parent tricycle was accessed
by Suzuki–Miyaura cross-coupling employing Buchwald’s
precatalyst. The boron complex of ageladine A exhibited strong fluorescence
that was greater than that of the natural product by a factor of ∼30
and that disappeared in the presence of 2-azido groups.
The synthesis of the ABCD tetracyclic partial structures of the fungal indole diterpenes janthitrem B, JBIR‐137, and shearinine G is reported. The route starts from 5‐formylated indoline that is coupled to a dihydropyran moiety, followed by Prins cyclization. A diene was obtained that was oxygenated in a divergent manner. The hydroxylated tetracyclic western half of janthitrem B was obtained in eight steps and 10 % overall yield. We also share our experience with alternative approaches passing via alkynylated precursors. This includes the gold‐catalyzed cycloisomerization of a 6‐ethynyl‐5‐prenylindoline.
The enantioselectives ynthesis of (À)-dihydroraputindole Di sr eported.T he key step is the desymmetrizing benzoylation of ap rochiral 1,3-diol employing Trost's ProPhenol catalyst system, which has been applied for the first time to ac yclic molecule carrying geminal hydroxymethyl groups. The cyclopenta[f]indoline system was assembled by Au(I)-catalyzed cyclization of an alkynylated indoline precursor.(À)-Dihydroraputindole Dw as obtained in 17 steps and 8% overall yield starting from dihydroxyacetone. In combinationw ith quantum chemical calculations of the ECD spectra, our synthesis allowed us to determine the absolutec onfiguration (5S,7R)o ft he natural product (+)-raputindole Df rom the Rutaceousp lant Raputia simulans. Scheme1.Structures of raputindoles A(1)and D(2)f rom the Peruvian rutaceous plant R. simulans,m odel of ap ossible ProPhenolcatalyst-substrate complex, and synthetic strategy.
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