Rhodium Catalysts with a Chiral Cyclopentadienyl Ligand Derived from Natural R‐Myrtenal

Abstract

A new chiral cyclopentadiene CpmyrH was synthesized from the natural terpene (R)‐myrtenal in 5 steps and about 40 % total yield. The key step was the reaction of vinyl‐dibromocyclopropane derivative with MeLi which provided the diene CpmyrH via Skattebøl rearrangement. The reaction of CpmyrH with [(cod)Rh(OAc)]2 gave the rhodium(I) complex (Cpmyr)Rh(cod) and subsequent oxidation with halogens X2 gave the rhodium(III) complexes [(Cpmyr)RhX2]2 (X = Br, I). Complex (Cpmyr)Rh(cod) in combination with benzoyl peroxide catalyzed the C–H activation of O‐pivaloyl‐phenylhydroxamic acid and its subsequent annulation with alkenes giving dihydroisoquinolones with high yield (70–90 %) but moderate enantioselectivity (16–36 % ee).

Synthesis of Overloaded Cyclopentadienyl Rhodium(III) Complexes via Cyclotetramerization of tert-Butylacetylene

“…Note that these reactions cleanly proceeded with the less bulky catalysts [Cp*RhCl 2 ] 2 , [(C 5 H 3 t Bu 2 )­RhCl 2 ] 2 , and [(C 5 H 2 t Bu 2 CH 2 t Bu)­RhCl 2 ] 2 . The reactions of 5 with 1-hexene or norbornene in the presence of the chiral catalyst 2a gave the corresponding dihydroisoquinolones 8 and 9 with 19% and 58% enantiomeric excesses (Scheme ), which again was lower than the stereoselectivity reached by the less bulky chiral catalysts. ,,, …”

“…32 Note that these reactions cleanly proceeded with the less bulky catalysts 19 The reactions of 5 with 1- hexene or norbornene in the presence of the chiral catalyst 2a gave the corresponding dihydroisoquinolones 8 and 9 with 19% and 58% enantiomeric excesses (Scheme 7), which again was lower than the stereoselectivity reached by the less bulky chiral catalysts. 12,18,34,35 At 120 °C complex 2b catalyzed the C−H activation of benzoic acid followed by annulation with diphenylacetylene and decarboxylation to give 1,2,3,4-tetraphenylnaphthalene (10) in a good 90% yield (Scheme 8). This result was different from the behavior of the [Cp*RhCl 2 ] 2 catalyst, which gave 3,4diphenylcoumarin under the same conditions, but was similar to the behavior of the simple RhCl 3 catalyst, which also gave 10, albeit in a lower yield of 40%.…”

Formation of a Naphthalene Framework by Rhodium(III)-Catalyzed Double C–H Functionalization of Arenes with Alkynes: Impact of a Supporting Ligand and an Acid Additive

“…The classical catalyst [Cp*RhCl 2 ] 2 showed moderate catalytic activity at 160 °C to give 6,7-dimethyl-1,2,3,4-tetraphenylnaphthalene ( 3aa ) in 55% yield (Table 1 , entry 1). Related rhodium(III) complexes with steric bulky cyclopentadienyl or indenyl ligands, such as [(Cp myr )RhBr 2 ] 2 , 11 [(C 8 H 3 t Bu 4 )RhBr 2 ] 2 , 12 and [(η 5 -tetrahydrofluorenyl)RhI 2 ] 2 , 13 demonstrated the same efficiency in this reaction (entries 2–4). In contrast, both the electron-deficient complex [Cp′RhCl 2 ] 2 (Cp′ = 1,3-(CO 2 Et) 2 -C 5 Me 3 ) reported by Tanaka 14 and the non-methylated complex [CpRhI 2 ] n , first introduced by our group, 15 effectively promoted the reaction with formation of 3aa in 90 and 96% yield (entries 5 and 6), respectively.…”

A Class of Readily Tunable Planar‐Chiral Cyclopentadienyl Rhodium(III) Catalysts for Asymmetric C–H Activation

“…The first type is based on chiral cyclopentadienyl (Cp) ligands prepared by linking or embedding the Cp motif to or into a certain chiral backbone (Figure 1a, type I). As shown in Figure 1b, a variety of elegant chiral Cp ligands have been prepared by this way during the last decade, including the artificial-enzyme-bound Cp A, [4] cyclohexane-fused Cp B, [3] biaryl Cp C, [5] cyclopentane-fused Cp D, [6] spirobiindanyl Cp E, [7] piperidine-fused Cp F, [8] myrtenal derived Cp G, [9] ferrocenyl Cp H, [10] and bicyclo[2.2.2]octane-fused Cp I. [11] The second type of chiral CpRh III catalysts is planar-chiral only, which is derived from non-chiral but prochiral Cp ligands (Figure 1a, type II).…”