Intramolecular absolute asymmetric

Kohmoto et al. reported an example of absolute asymmetric synthesis involving the intramolecular [4 + 4] photocycloaddition of 9-anthryl-/V-(naphthylcarbonyl)-... 

Since the concept of topochemically controlled reactions was established, various approaches to asymmetric synthesis using a solid-state reaction have been attempted, most actively by the research group at the Weismann Institute. Their studies have been concerned with the bimolecular reactions of chiral crystals in the solid state. In these studies, successful absolute asymmetric synthesis has been performed by using topochemically controlled four-centered photocyclodimerizations of a series of unsymmetrically substituted diolefin crystals. Research on reactivity in the crystalline state has been extended in recent years to a variety of new systems, and many absolute asymmetric syntheses have been provided. Successful examples of absolute asymmetric synthesis using chiral crystals are listed in Tables 2 to 4, which are divided into three categories intermolecular photoreaction in the solid state (Table 2), intramolecular photoreaction in the solid state (Table 3, A-D), and asymmetric induction in the solid-gas and homogeneous reactions (Table 4). 

Kohmoto et al. reported a fine example of absolute asymmetric synthesis involving the intramolecular [4 4- 4] photocycloaddition of 9-anthryl-Af-(naph-thylcarbonyl)carboxamide derivatives 42a-g in the solid state (Scheme 20) [26]. Out of seven carboxamides examined, 42a, 42e7 rid 42g showed intramolecular photocycloaddition in the solid state to give the [4 + 4] cycloadducts 43a, 43e, and 43g in almost quantitative yields after complete conversion and 42f gave 43f in 9% yield (Table 9). However, 42b, 42c, and 42d were unreactive. The crystals... 

Absolute asymmetric syntheses by irradiation of chiral crystals, now extended to intramolecular reactions, [27] support the assumption of the prebiotic origin of natural chirality. The chemical mechanisms here appear to be so conclusive and efficient that they should in any case be retained besides the complicated physical interpretations. [1, 2] It must be remembered that of the 230 space groups 65 are chiral and that of these P2i2i2i and P2i belong to the five most frequent in the organic crystals. 

Sakamoto reported the absolute asymmetric cyclobutane formation via intramolecular [2 + 2] photocycloaddition of iV, Af-diallyl-4-methyl-l-pro-pyl-2-quinolone-3-carboxamide (50) in chiral crystalline state. He also found the two-step reaction involving hydrogenation and intermolecular photocycloaddition of (50) with alkenes (53) afforded chiral cyclobutanes (54) at a low temperature (Scheme 17). ... 

Following Uskokovic s seminal quinine synthesis [40], Jacobsen has very recently reported the first catalytic asymmetric synthesis of quinine and quinidine. The stereospecific construction of the bicyclic framework, introducing the relative and absolute stereochemistry at the Cg- and expositions, was achieved by way of the enantiomerically enriched trans epoxide 87, prepared from olefin 86 by SAD (AD-mix (3) and subsequent one-pot cyclization of the corresponding diol [2b], The key intramolecular SN2 reaction between the Ni- and the Cg-positions was accomplished by removal of the benzyl carbamate with Et2AlCl/thioanisole and subsequent thermal cyclization to give the desired quinudidine skeleton (Scheme 8.22) [41],... 

Dauben et al. (15) applied the Aratani catalyst to intramolecular cyclopropanation reactions. Diazoketoesters were poor substrates for this catalyst, conferring little asymmetric induction to the product, Eq. 10. Better results were found using diazo ketones (34). The product cyclopropane was formed in selectivities as high as 77% ee (35a, n = 1). A reversal in the absolute sense of induction was noted upon cyclopropanation of the homologous substrate 34b (n = 2) using this catalyst, Eq. 11. Dauben notes that the reaction does not proceed at low temperature, as expected for a Cu(II) precatalyst, but that thermal activation of the catalyst results in lower selectivities (44% ee, 80°C, PhH, 35a, n = 1). Complex ent-11 may be activated at ambient temperature by reduction with 0.25 equiv (to catalyst) DIBAL-H, affording the optimized selectivities in this reaction. The active species in these reactions is presumably the aluminum alkoxide (33). Dauben cautions that this catalyst slowly decomposes under these conditions. 

Although the asymmetric total syntheses developed by Nicolaou and by Shair provide easy routes to enantiomerically pure CP compounds, the target molecules (+)-CP-263,114 (ent-1) and (—)-CP-225,917 (ent-2) are only the enantiomers of the natural occurring phomoidrides. After the establishment of the absolute configuration of the CP molecules by chemical synthesis, the focus of synthetic interest is the asymmetric total syntheses of (—)-CP-263,114 (1) and (-l-)-CP-225,917 (2). The first total synthesis furnishing (—)-CP-263,114 (1) as the correct enantiomer has recently been reported by Fukuyama et al. [23]. As the stereoselectivitydetermining step, an intramolecular Diels-Alder reaction was chosen, similar to that in Nicolaou s synthesis (Figure 11). The Diels-Alder precursor 42 is prepared in four easy... 

The asymmetric intramolecular crossed benzoin reaction catalysed by a chiral triazolium salt has been used to synthesise 3-hydroxychroman-4-ones 34 in good to high yields and ee. The absolute configuration at the quaternary stereocentre C-3 has been shown to be S by X-ray analysis of the camphanyl ester <06SL2431>. Both enantiomers of 2-(2-phenylethyl)chroman-4-one, flindersiachromanone, have been obtained from racemic l-phenylhex-5-en-3-ol after resolution via lipase-catalysed acetylation <06H(68)483>. 

An intramolecular diastereoselective Refor-matsky-type aldol approach was demonstrated by Taylor et al. [47] with an Sm(II)-mediated cy-clization of the chiral bromoacetate 60, resulting in lactone 61, also an intermediate in the synthesis of Schinzer s building block 7. The alcohol oxidation state at C5 in 61 avoided retro-reaction and at the same time was used for induction, with the absolute stereochemistry originating from enzymatic resolution (Scheme II). Direct re.solution of racemic C3 alcohol was also tried with an esterase adapted by directed evolution [48]. In other, somewhat more lengthy routes to CI-C6 building blocks, Shibasaki et al. used a catalytic asymmetric aldol reaction with heterobimetallic asymmetric catalysts [49], and Kalesse et al. used a Sharpless asymmetric epoxidation [50]. 

The first enantioselective total synthesis of ( )-7,8-epoxycembrene C (33) was achieved via a general approach by employing an intramolecular McMurry coupling and Sharpless asymmetric epoxidation as key steps from readily available starting material. The syntheses presented here verified the absolute stereochemistry assignment of the epoxy configuration of 33 as assumed (1R,8R) (Scheme 6-20). °... 

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