Stereogenic centres, contiguous

In another context, Davies et al. have developed the Rh2(-S -DOSP)4-catalysed decomposition of vinyldiazocarbonyl derivatives in the presence of vinyl ethers.The corresponding chiral cyclopentenecarboxylates were formed in high enantioselectivities of up to 99% ee with the full control of the relative stereochemistry at up to three contiguous stereogenic centres, as depicted in Scheme 10.9. 

The Plaquevent group achieved a new and efficient method for the approach to both enantiomers of methyl dihydrojasmonate 47 by asymmetric Michael addition under solid-liquid phase-transfer catalysis. The main advantages of their procedure are the solvent-free system and the creation of two contiguous stereogenic centres in one step. The authors proposed a plausible mechanism with a transition state composed of substrate 45 and catalyst, quinine-, or quinidine-derived PTC catalyst (48a, 49a), in which hydrogen bonding ensures the proximity of the reactive centres and significantly stabilises the transition state (Scheme 16.14). ... 

Cyclopentanes with four contiguous stereogenic centres were assembled with >20 1 dr and <99% ee from enals R CH=CHCHO and -unsaturated a-ketoesters R CH=CHC0C02R, activated by chelation to (Pr 0)4Ti, in a reaction catalysed by NHCs. ... 

Even though they are achiral, meso compounds are of some value as substrates in asymmetric synthesis, since, upon enantioselective reaction, they give chiral products with two contiguous stereogenic centres (see sections 6.5.2 and 6.5.3). 

In addition to the amino acid derived amino alcohols mentioned above, two other amino alcohols have been widely used ( R, 25)-ephedrine (8) which is a naturally occurring plant alkaloid, and the (5, 5)-amino diol (9) which is produced microbiologically as a byproduct from the manufacture of the antibiotic chloramphenicol. Note the presence of two adjacent [or contiguous] stereogenic centres in both these molecules, a useful feature also present in two of the amino acids, (5,5)-isoleucine (10) and (25,3/ )-threonine (11). The (/ )-amino alcohol (12) is also readily available in enantiomerically pure form. 

The domino Michael/aldol reaction of 3-halogeno-l,2-diones (273) (X = Cl, F) to a,fi-unsaturated aldehydes RCH=CHCH=0 (R = aryl, heteroaryl), catalysed by the prolinol derivatives (256), has been developed as a method for the construction of cyclopen- tanones (274) with four contiguous stereogenic centres (<94% ee, >20 1 dr)P ... 

The catalytic asymmetric /-selective Diels-Alder annulation of a, -unsaturated /-butyrolactams with enones provided a synthesis of, y-functionalized bridged bi-or tri-cyclic dihydropyranopyrrolidin-2-ones in one step (up to 98% yield, >20 1 dr, and 99% ee) The inverse-electron-demand aza-Diels-Alder cycloaddition 0 of A-aryl-a,/0-unsaturated ketimines with enecarbamates in the presence of chiral bifunctional phosphoric acids produced 4,5,6-trisubstituted 1,4,5,6-tetrahydropyridines having three contiguous stereogenic centres in up to 84% yield, 95 5 dr, and 95% 5-Alkenylthiazoles react as in-out dienes with e-poor dienophiles in polar 44-2- 0 cycloaddition reactions. The cycloadditions are site selective. The mechanism is thought to lie between a concerted but highly asynchronous process and a stepwise process. 

The [ RhCl(CO)2 2]-catalysedring opening ofiJandZ l-cyclopropylocta-l,2,6-trienes has been reported to give a,x-4,5-dimethylbicyclo[4.3.0]nona-l(9),2-dienes with three contiguous stereogenic centres (Scheme 152). 

Tiu-ks M, Fairweather KA, Scopelliti R, Vogel P. Efficient asymmetric synthesis of long-chain polyketides containing up to ten contiguous stereogenic centres by doublechain elongation. Eur. J. Org. Chem. 2011 (18) 3317-3328. 

A computational and experimental study of the oxy-Cope rearrangement of aldol products has been reported (Scheme 22) and a diastereoselective oxy-Cope/ene/Claisen reaction for the synthesis of decalin frameworks possessing four contiguous stereogenic centres has been applied. The aza-Cope/Mannich reaction has been reviewed. ... 

Enynes with ester functions in the tethering chain and substituted allylic carbons have also been subjected to kinetic resolution experiments, analogous to those mentioned in Fig. 10.19. This strategy affords an efficient and general asymmetric method for the synthesis of polyfunctional lactones with two contiguous stereogenic centres (Fig. 10.21) [33]. 

Allylic strain is employed in the Patemo-Biichi reaction of a silyl enol ether and benzaldehyde.79 Using a bulky or polar substituent y to the ether as stereogenic locus, diastereomerically pure oxetanes with four contiguous chiral centres have been prepared. 

Building on this chemistry, the same authors developed a novel four-component reaction of p-hydroxybenzaldehyde derivatives, benzylamine derivatives, fumaric acid monoethyl ester and isonitriles in water under microwave irradiation to give natural product-like 5,5,6-fused azaspiro tricycle systems 16 as the main products [11]. This transformation can be assmned to proceed through addition of a final aza-Michael step to the previously developed Ugi/Michael domino sequence, and generates six contiguous bonds and fonr stereogenic centres, including one... 

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