Asymmetric Rhodium‐Catalyzed Hydrogenation Meets Gold‐Catalyzed Cyclization: Enantioselective Synthesis of 8‐Hydroxytetrahydroisoquinolines

Abstract

Different furyl-substituted (Z)-dehydroamino acid derivatives were hydrogenated with the rhodium/Mandyphos(OMe)-system to give enantiomeric excesses between 80 and 98 %. The absolute configuration of the newly formed stereogenic center was determined by anomalous diffraction to be R. These chiral furyl alanines were transferred into 8-hydroxytetrahydroisoquinolines by employing gold-catalyzed arene synthesis as the key step. During the latter reaction sequence, also including either a propargylation or a reduction, a protection of the hydroxy group, and a subsequent propargylation, no racemization of the stereogenic center was observed. With very electron-rich furans, instead of the 8-hydroxytetrahydroquinolines as products, furans anellated to seven-membered rings with exocyclic C-C double bonds are formed under the same reaction conditions.

Synthesis, Electrochemistry, Crystal Structures, and Optical Properties of Quinoline Derivatives with a 2,2′‐Bithiophene Motif

“…The preparation of substituted quinolines under microwave irradiation has also been widely explored over the last several years. [27][28][29][30] The preparation of quinoline derivatives in the presence of Au I complex, [28] Zn(OTf) 2 , [29] and In(OTf) 3 [30] under microwave irradiation have been described. To our knowledge, although several quinolines with thiophene moieties have been synthesized, only a few with a 2,2Ј-bithiophen-5-yl moiety have been reported; however, 2-(thiophen-2-yl)quinoline is known.…”

Synthesis of Tyrosine‐Derived Tetrahydroisoquinolines by Lewis Acid Catalyzed Cyclization of N‐(Phenylsulfonyl)alkyloxazolidinones

“…As can be seen from Table 1, the ring closure of starting sulfones 11a-c and 12a-c proceeded uneventfully (Table 1, Entries 1-3, 9-11). Crotyl-substituted compound 12d, however, did not react and was reisolated in 68 % yield, whereas analogous m-tyrosine-based derivative 11d gave the product in 19 % yield (Table 1, Entries 4,12). In contrast, from benzyloxymethyl-substituted oxazolidinones 11e and 12e, the reaction of tyrosine derivative 12e afforded tricyclic compound 14e, whereas 13e was not formed (Table 1, Entries 5, 13).…”

“…[11] Hashmi used substituted furylalanine derivatives in Au-catalyzed cycloisomerizations. [12] Upon searching for suitable methods we were 5590 radical reduction conditions by using Bu 3 SnH/AIBN. Tetrahydroisoquinolines 13 and 14 were isolated as single diastereomers whose trans configuration was confirmed by Xray crystal structure analysis.…”

Gold(I)‐Catalyzed Tandem Rearrangement–Nucleophilic Substitution of α‐Acetoxy Alkynyl Oxiranes or Aziridines: Efficient Approach to Furans and Pyrroles

“…In contrast, treatment of 1a with benzyl alcohol resulted in the formation of benzyloxy furan 2g in high yield (Table 2, Entry 8). With the perspective to induce the formation of highly substituted phenols through a cascade reaction, similar to the report of Hashmi, [10] we tried to introduce a propargyl moiety adjacent to the furan. Epoxyalkyne 1a was thus submitted to the reaction conditions in the presence of propargyl alcohol.…”