Heterocyclic optically active

Polymers from Novel Monomers.—Novel monomers which have been polymerized recently by cationic mechanisms may be categorized as follows oxygen heterocycles, optically active monomers, and bifunctional monomers. 

Pubhcations have described the use of HFPO to prepare acyl fluorides (53), fluoroketones (54), fluorinated heterocycles (55), as well as serving as a source of difluorocarbene for the synthesis of numerous cycHc and acycHc compounds (56). The isomerization of HFPO to hexafluoroacetone by hydrogen fluoride has been used as part of a one-pot synthesis of bisphenol AF (57). HFPO has been used as the starting material for the preparation of optically active perfluorinated acids (58). The nmr spectmm of HFPO is given in Reference 59. The molecular stmcture of HFPO has been deterrnined by gas-phase electron diffraction (13). 

Oxirane (1) and methyloxirane (3) are miscible with water, ethyloxirane is very soluble in water, while compounds such as cyclopentene oxide and higher oxiranes are essentially insoluble (B-73MI50501) (for a discussion of the solubilities of heterocycles, see (63PMH(l)l77)). Other physical properties of heterocycles, such as dipole moments and electrochemical properties, are discussed in various chapters of pmh. The optical activity of chiral oxiranes has been investigated by ab initio molecular orbital methods (8UA1023). 

Racemic and optically active a-aminophosphonic acids, derivatives of various heterocycles 97ZOR1605. 

Controlled racemization of optically active heterocycles 97T9417. 

Asymmetric olefination using optically active P,0-heterocycles as reagents 98YGK521. 

Synthesis of optically active selenium and tellurium heterocycles and their application for asymmetric synthesis 97OPP603. 

The Enders method has also been used as a key step in the synthesis of optically active Ar-heterocycles. The use of cyclic 1,3-diketones for the preparation of the SAMP or RAMP lithium azaenolates is shown by the synthesis of substituted 4,6,7,8-tetrahydro-2,5(l//,3//)-quinolinediones 2. Michael addition of 1 with, for example, benzylidene propanedioates followed by removal of the auxiliary and lactamization gives 2 with > 98% ee201. 

In Table IV some physical data and spectral characteristics of 6,7-secoberbines are listed. Only methyl corydalate (55) is optically active. Formula 55 presents the spatial structure of this compound, deduced by Nonaka et al. (65) and confirmed by Cushman et al. by both correlation with (+)-mesotetrahydrocorysamine (72) (<5S) and total synthesis (69). It is difficult to find common characteristic features in both the mass and H-NMR spectra of these alkaloids because they differ significantly from each other in their structures. On one hand, corydalic acid methyl ester (55) incorporates a saturated nitrogen heterocycle, while the three aromatic bases (56-58) differ in the character of the side chain nitrogen. For example, in mass fragmentation, ions of the following structures may be ascribed to the most intensive bands in the spectrum of 55 ... 

In the construction of C=N bond-containing compounds, such as nitrogen heterocycles, the aza-Wittig methodology has received increased attention as the method of choice [7]. Thus, an easy access to optically active (-)-vasicinone (7-15), a pyr-rolo[2,l-fc]quinazoline alkaloid which is used in indigenous medicine [8], was... 

Abstract This review presents the synthesis of selected five-membered phosphorus heterocycles containing a stereogenic phosphorus in an optically active form. Their utility in a few asymmetric reactions is also briefly mentioned. 

Hoveyda and co-workers also tested optically active A-heterocyclic carbenes and their silver complexes in copper-catalyzed reactions of allylic phosphates with dialkylzincs.402 The ratios of Sn2 SN2 products were higher than 98 2 and the ee varied from 34% to 98%. 

Asymmetric aza Diels-Alder reactions provide a useful route to optically active heterocyclics such as piperidines and tetrahydroquinolines.45 Although successful examples of diastereoselective approaches had been reported as early as 10 years ago,46 only recently have enantioselective reactions been accomplished.47 For example, the reaction of chiral amine-derived aromatic imine 115 with Brassard s diene 116 gives adduct 117 with up to 95% diaster-eoselectivity (Scheme 5-37).48... 

If the alkenes and acetylenes that are subjected to the reaction mediated by 1 have a leaving group at an appropriate position, as already described in Eq. 9.16, the resulting titanacycles undergo an elimination (path A) as shown in Eq. 9.58 [36], As the resulting vinyltitaniums can be trapped by electrophiles such as aldehydes, this reaction can be viewed as an alternative to stoichiometric metallo-ene reactions via allylic lithium, magnesium, or zinc complexes (path B). Preparations of optically active N-heterocycles [103], which enabled the synthesis of (—)-a-kainic acid (Eq. 9.59) [104,105], of cross-conjugated trienes useful for the diene-transmissive Diels—Alder reaction [106], and of exocyclic bis(allene)s and cyclobutene derivatives [107] have all been reported based on this method. 

The phosphine-phosphite BINAPHOS ligand was first used in the Rh-catalyzed asymmetric hydroformylation of heterocyclic olefins such as 2,5-dihydrofuran, 3-pyrroline derivatives, and 4,7-dihydro-1,3-dioxepin derivatives. It provided the optically active aldehydes as single products with enantioselectivity between 64-76% ee. In the hydroformylation of 2,5-di-... 

Reactions.—Alkaline Hydrolysis. The first total resolution of a heterocyclic phosphonium salt containing an asymmetric phosphorus atom (128) has been reported, providing ready access to optically active phospholan derivatives of value for studies of the stereochemistry of nucleophilic displacement at phosphorus.124 Alkaline hydrolysis of (128) proceeds with retention of configuration at phosphorus to form the oxide (129). Stereochemical studies in the phospholan series have also been facilitated by the X-ray investigation125 of an isomer of l-iodomethyl-l-phenyl-3-methylphospholanium iodide, which is shown to have the structure (130). 

In view of our interest in heterocyclic chemistry 44), a study was begun which had as its scope the synthesis and resolution of phenylthio-phenes capable of existing in two optically active forms due to restricted rotation about their pivot bonds. Two possibilities for these phenyl-thiophenes existed ... 

The heterocyclic component in the leaving group offers possibilities for introduction of chirality. Optically active oxazolin-2-yl and thiazolin-2-yl allyl thioethers 7 were thus chosen as substrates (Scheme 8.8) [17]. 

Polyamino acids are easy to prepare by nucleophUe-initiated polymerisation of amino acid JV-carboxyanhydrides. Polymers such as poly-(L)-leucine act as robust catalysts for the epoxi-dation of a wide range of electron-poor alkenes, such as y-substituted a,Ji-unsaturated ketones. The optically active epoxides so formed may be transformed into heterocyclic compounds, polyhydroxylated materials and biologically active compounds such as dUtiazem and taxol side chain. 

Volume 64 of our series consists of six chapters covering an exciting range of topics in contemporary heterocyclic chemistry. M. TiSler and P. Kolar (Ljubljana, Slovenia) review applications of various amino acids in the synthesis of chiral heterocycles which have become of great importance as synthons for the preparation of a variety of optically active derivatives. 

The enantioselective hetero-Diels-Alder (HDA) reaction of carbonyl compounds with 1,3-dienes represents an elegant access to optically active six-membered oxo-heterocycles. Since the pioneering work of Rawal et al. in 2003 [55], the enantioselective HDA reaction catalyzed by diols (such as TADDOLs) has become a flourishing field of research [56]. 

The scope was illustrated with 35 examples using various P-ketoesters as well as acetylacetone as 1,3-dicarbonyl compound. The use of aliphatic a,P-unsaturated aldehydes resulted in low yield and inferior enantioselectivity. Transformation of the DHP products into other optically active heterocyclic... 

A vast array of piperidine containing cores, both natural and synthetic, are of biological and medicinal interest. These heterocyclic scaffolds have been the subjects of considerable synthetic efforts, especially for the construction of optically active compounds. In this context, Khan et al. reported a catalytic bromodi-methylsulfonium bromide (BDMS) three-component reaction of 1,3-dicarbonyls with aromatic aldehydes and aromatic amines for a facile access to highly functionalized piperidines (Scheme 24) [104]. This strategy is an interesting illustration of... 

Recently, an asymmetric version of this reaction has been reported by Gong and co-workers, allowing an efficient access to highly enantiomerically enriched 4-aryl-substituted 1,4-DHPs [152]. Thus, the use of chiral phosphoric acids as catalysts allowed the preparation of the desired products with enantiomeric excesses up to 97% (Scheme 53). To illustrate the importance of this asymmetric cyclization reaction, the authors developed the synthesis of some optically active heterocycles... 

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