Chiral ligands terpenes

A second group of ligands has the asymmetric center not at the phosphorus, but in an alkyl side chain. These are easy to obtain from a chiral product (terpene, sugar, etc.) by displacement of a leaving group by the diphenylphosphide anion Ph2P (Table 2). 

Uros Groselj was born in Kranj, Slovenia, in 1975. He studied chemistry at the University of Ljubljana and received his B.Sc. in 2000. He continued his studies under the supervision of Professor Dr. Jurij Svete and received his Ph.D. in 2004. Currently, he is working as a researcher in the group of Professor Dr. Branko Stanovnik at the Faculty of Chemistry and Chemical Technology, University of Ljubljana. His research interests encompass synthesis of heterocyclic compounds, stereoselective synthesis, chemistry of terpene enaminones, cycloadditions, and synthesis of chiral ligands. 

Terpenes are found primarily in higher plants, less commonly in animals. They are often isolated by steam distillation or extraction. The major commercial applications of terpenes are as fragrance and flavoring agents. Terpenes often serve in organic chemistry as versatile carriers of chiral information. For example, (-)-a-pinene (2) is commonly used as a ligand for chiral induction. 

Many chiral auxiliaries are derived from 1,2-amino alcohols.7 These include oxazolidinones (l),7-9 oxazolines (2),10 11 bis-oxazolines (3),1213 oxazinones (4),14 and oxazaborolidines (5).15-17 Even the 1,2-amino alcohol itself can be used as a chiral auxiliary.18-22 Other chiral auxiliaries examples include camphorsultams (6),23 piperazinediones (7),24 SAMP [(S)-l-amino-2-methoxy-methylpyrrolidine] (8) and RAMP (ent-8),25 chiral boranes such as isopinocampheylborane (9),26 and tartaric acid esters (10). For examples of terpenes as chiral auxiliaries, see Chapter 5. Some of these auxiliaries have been used as ligands in reagents (e.g., Chapters 17 and 24), such as 3 and 5, whereas others have only been used at laboratory scale (e.g., 6 and 7). It should be noted that some auxiliaries may be used to synthesize starting materials, such as an unnatural amino acid, for a drug synthesis, and these may not have been reported in the primary literature. 

Supramolecular coordination compounds with chiral pyridine and polypyridine ligands derived from terpenes 03CCR(242)87. 

A temperature-dependent NMR spectroscopic study revealed that in solution this species shows dynamic intramolecular coordination of the pendant ether groups, facilitating partial dissociation into the ionic [(3a)2Zr(OTf)]OTf. In the case of the unstable analogues containing cyclopentadienyl ligands 8a and 8b, which bear the much bulkier chiral terpene-... 

Ddii.c. Complexes with Chiral TT-Allyl Ligands. Chirality can be introduced to the TT-allyl moieties of the palladium complexes. Some representative examples are shown in Figure 11. The chiral sources of these 7r-allyl species are chiral terpenes. The terpenes (-)-(3-pinene, pinadiene (for 60), and (+)-3-carene (for 61) reacted with Pd(OAc)2 to give 60, ° and 61, ° respectively. Meanwhile, these terpenes reacted with... 

The BV transformations with chiral metal complexes are based on either transition metals such as Cu [37b, 40, 41], Pt [42, 43], Co [44], Pd [45], Zr [46], Hf [47] or nontransition metals such as Mg [48] and Al [49]. For example, Kocovsky and coworkers have developed a series of new terpene-derived pyridinephosphine ligands, whose complexes with Pd(II) have been proven to catalyze the BV oxidation. Prochiral cyclobutanones (1) were oxidized at low temperature (—40°C), with 5 mol % catalyst loading and the urea-H202 complex as the stoichiometric oxidant to give lactones 2 in good yields and up to 81% ee (Eq. (10.5)) [50],... 

Subsequently, Carreira, and coworkers [35] disclosed their results on the synthesis of a different chiral diene-metal complex. Using a terpene-derived diene ligand complexed to iridium, high enan-tioselectivity was achieved in a catalytic kinetic resolution of allylic carbonates. Unfortunately, this... 

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