Lactone concept

Acid treatment of a 3 1 mixture of murrayafoline A (7) and koenoline (8) led to chrestifoline A (192) in 70% yield. Addition of murrayafoline A (7) to a mixture of 1057 and lithium aluminum hydride in ether and dichloromethane afforded bismurrayafoline-A (197) in 19% yield (662) (Scheme 5.166). In addition to the aforementioned methods, the same group also reported a stereoselective synthesis of axially chiral bis-carbazole alkaloids by application of their "lactone concept" (663) and a reductive biaryl coupling leading to 2,2 -bis-carbazoles (664). 

The lactone concept is not restricted to the simple model biaryl synthesis presented here. It has been successfully expanded to a broad series of structurally diverse biaryl substrates (e.g., lactones with additional stereocenters and functional groups, configurationally stable lactones, seven-membered lactones, and again configurationally unstable biaryl hydroxy aldehydes ), to different activation modes in the ring-opening step (e.g., use of metallated nucleophiles, carbonyl activation by Lewis acids, (Ti -complexation, etc.), and for various strategies of stereoselection (e.g., external vs. internal asymmetric induction). ... 

Within the lactone concept, Uemura s group has shown that the element of planar chirality was excellently suited for transferring chiral information to the axis. Treatment of the configurationally unstable lactone depicted in Scheme 5.14, which bears an i -configured 1-hydroxyethyl substituent ortho to... 

Application of the Lactone Concept to Configurationally Unstable Compounds other than Biaryl Lactones... 

The strategy based on the lactone concept is not restricted to biaryl lactones as substrates, but can be applied to other configurationally unstable biaryls such as biaryl hydroxy aldehydes. As an example, the reduction of biaryl hydroxy aldehydes in the presence of a CBS catalyst and catecholborane yielded the corresponding alcohols, as shown in Scheme 5.21. ... 

Alkali mentholates were also involved in the first stereoselective synthesis of bismurrayaquinone A, an axially chiral biscarbazole alkaloid (Scheme 5.42). Naphthylisoquinoline alkaloids show interesting bioactivities, including strong anti-malarial and anti-leishmanial properties. Some of their dimers also exhibit high anti-HIV activities. The lactone concept allowed an efficient synthetic access to this class of alkaloids, such as korupensamines A and B (Scheme... 

The lactone concept also allowed easy access to monodentate phosphine ligands with sterically hindered biaryl axes, which catalysed the asymmetric hydrosilylation of styrenes in the presence of palladium (Scheme 5.49). ... 

Finally, the lactone concept was extended to the synthesis of two-fold lactone-bridged teraryls which may be suitable precursors for the formation of... 

The synthesis in Scheme 13.41 is also built on the desymmetrization concept but uses a very different intermediate. cA-5,7-Dimethylcycloheptadiene was acetoxylated with Pd(OAc)2 and the resulting all-cA-diacetate intermediate was enantioselectively hydrolyzed with a lipase to give a monoacetate that was protected as the TBDMS ether. An anti Sw2 displacement by dimethyl cuprate established the correct configuration of the C(2) methyl substituent. Oxidative ring cleavage and lactonization gave the final product. 

The regio- and stereo-selective functionalization of aldonolactones yields optically active lactones, which are important precursors in natural product synthesis. Concepts such as chiral templates and chirons, derived from carbohydrates, have been ingeniously and widely applied in synthesis (233). Among the commercially available aldonolactones, D-ribono-1,4-lactone is... 

It is astonishing that Bledius arenarius represents the only species which does not fit into this concept, because its toluquinone is dissolved only in de-canoic acid and octyl octanoate (Fig. 4). However, B. opacus and B. subterraneus keep an intermediate position because they secret both alkenes/lactones and acids which are also found in B. arenarius [123]. 

The application of thermomorphic solvent systems as a new recycUng concept was investigated in various C - C bond-forming reactions. Therefore methods for a systematic choice of solvent combinations were developed. In addition to common organic solvents more unusual solvents Hke cycHc carbonates, pyrroUdones, polyethylene glycols and lactones were used in the investigations. The phase behaviour of the new solvent systems was determined by cloud titrations. From these experiments information about the temperature dependency and an appropriate composition for the reactions could be obtained. The results were used in the development of an expert system for the solvent selection. 

Later, Kricheldorf and coworkers extended the concept of the aluminum alkox-ide-initiated ROP of lactones to a set of other metal alkoxides such as tin(lV) [23-25], titanium, and zirconium alkoxides. As a rule, the polymerization takes place according to the same coordination-insertion mechanism shown in Fig. 12. 

In the present study, the novel concept of the Lewis acid assisted living polymerization with the aluminum porphyrin-methylaluminum diphenolate (3) system was successfully extended from the accelerated living addition polymerization of alkyl methacrylates to the accelerated living ring-opening polymerizations of lactones. 

As described in the above section, the concept of immortar polymerization in the polymerizations of epoxides and lactones initiated with aluminum porphyrin in the presence of a protic compound has been developed where polymers of uniform molecular weight are formed with the number of the molecules equal to the sum of those of aluminum porphyrin and the protic compound [83]. This is due to the rapid, reversible chain transfer reaction between the molecules of growing polymer and the protic compound, which takes place much faster than the propagation reaction. In the presence of 1-propanethiol (PrSH) as the protic compound, the polymerization of PO ([PO]o/[HX]o/[17 (X=SPr)]o=400/10/l) proceeded to 93% conversion in 45.5 h at room temperature under irradiation, producing a polymer with Mn and Mw/Mn of 1660 and 1.11, respectively. The number of the polymer molecules relative to that of 17 (X=SPr) as estimated from Mn and the yield of the polymer [84], is... 

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