Enantioselective Synthesis of a <i>trans</i>-7,8-Dimethoxycalamenene

Werle, Susen; Fey, Thorsten; Neudörfl, Jörg‐M.; Schmalz, Hans‐Günther

doi:10.1021/ol071228v

Cited by 54 publications

(33 citation statements)

References 24 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The obtained 3-methyl-1,2-dialkoxybenzenes 6a, b were subjected to a Bouveault formylation to 7a, b. The formylation was neither regioselective nor chemoselective; the CH 3 group was also attacked by DMF [15,16]. Consequently the yields of 7a, b were low.…”

Section: Resultsmentioning

confidence: 99%

Preparation of 1,2,5,6,9,10-Hexaalkoxyhexahelicenes

Schwertel¹,

Hillmann²,

Meier³

2013

Zeitschrift Für Naturforschung B

View full text Add to dashboard Cite

show abstract

Section: Resultsmentioning

confidence: 99%

Preparation of 1,2,5,6,9,10-Hexaalkoxyhexahelicenes

Schwertel¹,

Hillmann²,

Meier³

2013

Zeitschrift Für Naturforschung B

View full text Add to dashboard Cite

show abstract

“…[13] This new class of readily available chiral ligands was then shown to possess a promising potential for asymmetric metal catalysis (especially Cu-and Rhcatalyzed transformations). [14] We therefore envisioned that such ligands could also serve in the Rhcatalyzed [4 + 2] cycloaddition of tethered diene-enes of type 1. We here report on the successful realization of this idea and the elaboration of an optimized protocol for such transformations.…”

Section: P Nmr and Esi-ms Measurements Indicated The Formation Of A [mentioning

confidence: 99%

Rhodium‐Catalyzed Enantioselective Intramolecular [4+2] Cycloaddition using a Chiral Phosphine‐Phosphite Ligand: Importance of Microwave‐Assisted Catalyst Conditioning

et al. 2011

Self Cite

View full text Add to dashboard Cite

The use of modular a,a,a',a'-tetraaryl-1,3-dioxolane-4,5-dimethanol (TADDOL)-and 1,1'-bi-2-naphthol (BINOL)-derived phosphine-phosphite ligands (L 2 *) in the asymmetric rhodium-catalyzed intramolecular [4 + 2] cycloaddition ("neutral" Diels-Alder reaction) of (E,E)-1,6,8-decatriene derivatives (including a 4-oxa and a 4-aza analogue) was investigated. Initial screening of a small ligand library led to the identification of a most promising, TADDOL-derived ligand bearing a phenyl group adjacent to the phosphite moiety at the arene backbone. In the course of further optimization studies, the formation of a new, more selective catalyst species during the reaction time was observed. By irradiating the pre-catalyst with microwaves prior to substrate addition high enantioselectivities (up to 93% ee) were achieved. The new cyclization protocol was successfully applied to all three substrates investigated to give the bicyclic products in good yield and selectivity. P NMR and ESI-MS measurements indicated the formation of a+ species as the more selective (pre-) catalyst.Keywords: asymmetric catalysis; chiral P,P ligands;cycloaddition; Diels-Alder reaction; enantioselectivity; rhodium(I) complexes Cycloadditions, such as the most prominent DielsAlder reaction, [1] open particularly powerful options for the construction of polycyclic systems in an atomeconomical fashion.[2] With the emergence of transition metal catalysis, the toolset of classical (pericyclic) cycloaddition chemistry has been greatly expanded and even "uncommon" types of (formal) cycloadditions, such as [2 + 2 + 2], [3] [2 + 2 + 1], [4] or [5 + 2][5]processes have been developed and applied as strategic key steps in natural product synthesis.[6]Transition metal catalysis also allows one to overcome certain limitations of the classical Diels-Alder reaction. For instance, so-called "neutral" DielsAlder reactions, involving non-activated dienes and dienophiles, often cannot be achieved under thermal (or Lewis acid-catalyzed) conditions. However, it has been shown that certain transition metal complexes are able to efficiently catalyze such transformations, in particular in cases where an alkyne (or allene) acts as the dienophile. [7] Intramolecular [4 + 2] cycloadditions of trienes of type 1 represent an interesting challenge, as the resulting hexahydroindenes (or their hetero analogues) of type 2 resemble relevant substructures of natural products (Scheme 1). As an important breakthrough, Livinghouse and co-workers reported in 1990 that the conversion of 1a to rac-2a could be achieved in high yield using [(i-C 3 HF 6 O) 3 P] 2 RhCl as a catalyst. [8] The chirogenic nature of this Rh-catalyzed transformation opens the possibility to perform it in an asymmetric fashion by using chiral ligands. A first enantioselective version was disclosed by Livinghouse who used DIOP in the synthesis of 2a (73% ee) [9] and 2b Scheme 1. Rh-catalyzed intramolecular [4 + 2] cycloadditions of trienes of type 1.

show abstract

“…[18] Noteworthy is the circumstance that 17 represents a rather demanding substrate which, in contrast to the parent unsubstituted styrene, only gave unsatisfying enantioselectivities ( 75 ee) under standard conditions when BINAP or our first generation ligand 1 was employed. We observed a pronounced effect of the substitution pattern at the ligand backbone and identified 10b as the most effective ligand so far, giving intermediate 18 with at least 93% ee.…”

Section: Chiral Diol Final Ligand a C H T U N G T R E N N U N G (Yielmentioning

confidence: 99%

“…We observed a pronounced effect of the substitution pattern at the ligand backbone and identified 10b as the most effective ligand so far, giving intermediate 18 with at least 93% ee. [18] Exploiting the efficient diversity-oriented synthetic scheme, further variation (optimization) of the ligand structure should be possible without unreasonable expenditure.…”

Section: Chiral Diol Final Ligand a C H T U N G T R E N N U N G (Yielmentioning

confidence: 99%

Modular Synthesis of Chiral Phosphine‐Phosphite‐Ligands from Phenolic Precursors: A New Approach to Bidentate Chelate Ligands Exploiting a PO to PC Migration Rearrangement

et al. 2008

Self Cite

View full text Add to dashboard Cite

An efficient and modular approach to bidentate phosphine-phosphite ligands formally derived from a 6-alkyl-2-phosphanylphenol, a chiral diol and phosphorus trichloride has been developed. In a key step, a borane-protected phosphinite, prepared from an o-bromophenol by O-phosphanylation, is reacted with n-butyllithium to afford the corresponding ortho-phosphanylphenol (as the stable borane adduct) through bromine-lithium exchange and anionic migration rearrangement. Treatment with phosphorus trichloride in the presence of a base and subsequent reaction of the in situ formed dichlorophosphite with a chiral diol (such as TADDOL or BINOL) affords the target P,P ligands in good overall yield (up to 60% over 4 steps). In contrast to an earlier approach, the new methodology is very general and tolerates bulky ortho-substituents. The reliability of the operationally convenient protocol was demonstrated in the synthesis of a library of 16 new phosphine-phosphite ligands, starting from different ortho-alkylphenols. The modular concept opens a rapid access to a broad variety of ligands and might be useful in the search for and structural optimization of suitable ligands for specific chirogenic transition metal-catalyzed transformations.

show abstract

Enantioselective Synthesis of a trans-7,8-Dimethoxycalamenene

Cited by 54 publications

References 24 publications

Preparation of 1,2,5,6,9,10-Hexaalkoxyhexahelicenes

Preparation of 1,2,5,6,9,10-Hexaalkoxyhexahelicenes

Rhodium‐Catalyzed Enantioselective Intramolecular [4+2] Cycloaddition using a Chiral Phosphine‐Phosphite Ligand: Importance of Microwave‐Assisted Catalyst Conditioning

Modular Synthesis of Chiral Phosphine‐Phosphite‐Ligands from Phenolic Precursors: A New Approach to Bidentate Chelate Ligands Exploiting a PO to PC Migration Rearrangement

Contact Info

Product

Resources

About