Davies optical activity

Optically active selenoxides are known to be unstable toward racemization. An optically active selenoxide having a steroidal frame was obtained for the first time by Jones and co-workers in 1970.7 Enantiomeric selenoxides were prepared by Davis et al. in 1983,8 and an enantiomerically pure selenoxide was isolated for the first time by us in 1989.9 Many optically active selenoxides, which are kinetically stabilized by bulky substituents, were synthesized over the last two decades, and their stereochemistry and stability toward racemization were studied.3,5,10 Recently, some optically active selenoxides, which were thermodynamically stabilized by the intramolecular coordination of a Lewis base to the selenium atom, have been isolated. Optically active selenoxides 1 and 2 were obtained by optical resolution on chiral columns, and their stereochemistry and stability toward racemization under various conditions were clarified (Scheme 1).11,12... 

This inference is checked stereochemically. If hydroperoxide produces alcohol at the expense of disproportionation of radicals not leaving the cage, the enantiomeric hydroperoxide should give alcohol that retains its optical activity. And this is what actually takes place (Davies and Feld 1958). 

Davies and Roberts7 have shown that the dibutyl ester of optically active 1-phenylethylboronic acid is cleaved by C7H15C02D in boiling diglyme to yield (—)-l-deuterioethylbenzene with 95 % retention of configuration. The acidolysis was suggested7 to proceed by mechanism SE2(cyclic), reaction (4),... 

Intermolecular cycloaddition reactions constitute an important and convergent route to piperidines and related compounds. The research group of Franklin Davis at Temple University published a novel route to optically active piperidines that proceeded through an imino Diels-Alder reaction with enantiomerically enriched compound 84 (Scheme 16) <02OL655>. On reaction with ftww-l,3-pentadiene, intermediate 85 was produced as a single diastereomer in 89% yield. Hydrogenation of this strained intermediate yielded the 2,6-disubstituted piperidine 86 in 75% yield. 

Asymmetric [2,3]sigmatropic rearrangements can proceed via optically active selenoxides. It has been shown that the Davis oxidant 158 can be used for the oxidation of selenides such as 172. The reaction product, after oxidation and rearrangement, is the allylic alcohol 173 formed with 35% ee (Scheme 50).279,282 Also Sharpless conditions (Ti(/ -PrO)4, (+)-DIPT, /-BuOOH) have been applied to this reaction and the product has been obtained in 69% ee. When, however, the phenyl selenide moiety in 172 is replaced with an or/ < -nitrophenyl selenide, the selectivity is increased to 92% ee in the allylic alcohol 173 using Sharpless conditions.296 Other selenides such as 2 -pyridyl or ferrocenyl selenides gave much lower selectivities. 

Chen G, Ensor CR, Bohner B (1966) The neuropharmacology of 2-(o-chlorophenyl)-2-methylaminocyclohexanone hydrochloride. J Pharm Exp Ther 152 332-339 Child KJ, Currie JP, Davis B et al. (1971) The pharmacological properties in animals of CT1341 - a new steroid anaesthetic agent. Br J Anaesth 43 2-24 Christensen HD, Lee IS (1973) Anesthetic potency and acute toxicity of optically active di-substituted barbituric acids. Toxicol Appl Pharmacol 26 495-503 Domenjoz R (1959) Anaesthesist 8 16... 

Soon after Kuhn s photodestruction experiments around 1930, Karagunis and Drikos tried to perform an asymmetric synthesis with an asymmetrically substituted triphenylmethyl radical, but there was no optical activity created [107]. In 1935 Davis and Heggie [108] reported a total asymmetric synthesis by addition of bromine to 2,4,6-trinitrostilbene (they found, however, a maximum curve of... 

The formation of 0-methylated metabolites of THP, and of berbine 124, with rat liver microsomal enzymes was investigated in some detail 212,213). It was shown by Davis and colleagues that intraventricular application of racemic and optically active THP and of berbine 124 led after 1 hr to the formation of metabolites which were identified and quantitated by GC-MS methods. The results are summarized in Fig. 30. It can be seen that O-methylation of the hydroxy group at C-6 in both enantiomers of THP and the racemate necessary to connect with norreticuline (121) only was a minor pathway, and that O-methylation of the hydroxy group at C-7 was the preferred route. 0-MethyIation of the hydroxy group at C-11 in berbine 124 was preferred over that at C-10, as was the O-methylation of the hydroxy group at C-2 over that at C-3. 

In later work (1964), Davis and Mann (11) prepared the stable colorless iodides LXVIII (R = CH3 and Cells) and LXIX. The iodide ion in the salt, LXVIII (R = CH3), was replaced in turn by nine optically-active anions, but again fractional crystallization gave no evidence of... 

LePage, J.N. Lindner, W. Davies, G. Seity, D.E. Karger, B.L. Resolution of the optical isomers of dansyl amino acids by reversed phase liquid chromatography with optically active metal chelate additives. Anal. Chem. 1979, 51 (3), 433-435. 

Davis, F. A., McCauley, J. P., Jr., Chattopadhyay, S., Harakal, M. E., Watson, W. H., Tavanaiepour, I. New synthetic applications of chiral sulfamides. Optically active sulfamyloxaziridines in the oxidation of nonfunctionalized substrates with high enantioselectivity. Stud. Org. Chem. (Amsterdam) 1987, 28, 153-165. 

For example Davis and An sari33 proposed a synthesis of optically active 39 (R = Me(Et)CH, R = Ph) by way of this kind of reaction. However, these authors never succeeded in performing the last step with classical bases. Moreover, with NaNH2, they obtained a mixture of ethylenic and saturated hydrocarbons (Scheme 17). 

McDonagh. A.M., Cifuentes, M.P., Humphrey. M.G., Houbrechts, S., Maes, J., Persoons, A., Samoc, M., Luther-Davies, B. Organometallic complexes for nonlinear optics Part 21. Syntheses and quadratic hyperpolarizabiUties of alkynyl complexes containing optically active l,2-bis(methylphenylphosphino)benzene ligands. J. Organomet. Chem. 610, 71-79 (2000)... 

Enolates of iron-acyl complexes have been studied extensively, especially by Davies and Liebeskind and their respective coworkers. The chiral complex [T) -CpFe(PPh3)(CO)COCH2R] is usually used it can be prepared in racemic or optically active form. The enolate usually has the anti conformation with regard to CO and Copper (Z)-enolates give predominantly syn aldols, whereas diethylalumin-... 

Prior to Davis and co-workers introduction of trans-( )-2-(phenylsulfonyl)-3-phenyloxaziridine (1) for direct enolate oxidation in 1984, there were several nonoxidative procedures for the formation of optically active a-hydroxy carbonyl compounds, but only one actively practiced oxidative method for the synthesis of such compounds.2... 

The utility of Davis chiral oxaziridine reagents has been more recently applied to the synthesis of optically active a-hydroxy phosphonates. Two groups have been largely responsible for developments in this area. Principally, Wiemer and co-workers have demonstrated the highly enantioselective hydroxylation of a series of benzyl phosphonates. As shown below for 69, hydroxylation makes use of oxaziridine 6, proceeding in moderate... 

Kossiakov and Bice 2) have shown that the energy of activation for the fission of a carbon-hydrogen bond is least at a tertiary carbon atom, the energy for this case being 2 kcaJ. less than for a secondary carbon atom and 4 kcal. less than for a primary carbon atom. It would therefore seem that, for work of this type, hydrocarbons containing one or more tertiary carbon atoms would be most suitable for study. Davies and Elton (S) showed that optically active 2-phenylbutane imdergoes racemization when adsorbed on charcoal, homolysis occurring at the tertiary carbon atom. 

Liebeskind and Davies " ° have independently developed the use of this chiral iron complex for enantioselective organic syntheses, particularly of a variety of optically active molecules. The reasons for this behaviour are that the complex is chiral-at-iron and one face is hindered by the PPha ligand reaction of these acyl-iron enolates occur with very high stereoselectivity (Scheme 3.7). 

Quinazolinone annelation of the 0-protected chiral pyrolidinone 74 (derived from L-aspartic acid) forms pyrrolo[2,l-fc]quinazohn-9(lH)-one 75 subsequent desilylation affords (S)-(-)-vasicinone 10, which is identical with the natural /-product (Scheme 16) [212,213]. Asymmetric oxidation of de-oxyvasicinone 11 (via the imine enolate) with either (R)- or (S)-Davis ox-aziridine reagent (lO-camphorsulfonyloxaziridine) [214,215] provides a convenient route to both enantiomers, thus confirming the recently revised stereochemistry of natural vasicinone (Scheme 16) [212,213]. Recently another approaches to optically active pyrrolo[2,l-fo]quinazolinones 10 have been reported by Kamal et al. (lipase-catalyzed resolution) [56], and Argade et aL (asymmetric synthesis from (S)-acetoxysuccinic anhydride) [216]. One-pot synthesis of 11, and related alkaloids has been also developed by utilizing microwave irradiation by Liu et al. [217]. Biogenetically patterned short-step synthesis of pyrroloquinazolinone alkaloids is well established by On-aka [218], and for many other synthesis, see the references cited in these papers. 

A diversity of thiolactams has been prepared from the corresponding lactams by use of LR or of the modified reagent (13). Monobactam analogs, e.g., the weakly antibacterial -thiolactam (93), have been prepared by thionation of suitably protected optically active /3-lactams with LR or Davy s reagent (2,4-bis (methylthio)-l,3,2,4-dithiadiphosphetane disulfide), deprotection and subsequent introduction of the side chain. Very recently, an efficient solid-phase synthesis of 1,3,4-trisubstituted /3-thiolactams has been described. The y-thiolactam (94) has been prepared as an intermediate for the synthesis of analogs of the acetylcholinesterase inhibitor huperzine B. Transformation of the quinoline alkaloid cytisine into its thio analog (95) enhanced its biological activity. ... 

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