Optically active bicyclic

In an extension of this work, the Shibasaki group developed the novel transformation 48—>51 shown in Scheme 10.25c To rationalize this interesting structural change, it was proposed that oxidative addition of the vinyl triflate moiety in 48 to an asymmetric palladium ) catalyst generated under the indicated conditions affords the 16-electron Pd+ complex 49. Since the weakly bound triflate ligand can easily dissociate from the metal center, a silver salt is not needed. Insertion of the coordinated alkene into the vinyl C-Pd bond then affords a transitory 7t-allylpalladium complex 50 which is captured in a regio- and stereocontrolled fashion by acetate ion to give the optically active bicyclic diene 51 in 80% ee (89% yield). This catalytic asymmetric synthesis by a Heck cyclization/ anion capture process is the first of its kind. 

In /cTf-butyl methyl ether, the optically active, bicyclic 2//-azepine 12 undergoes a suprafacial [1,5]-H shift to yield the isomeric, non-racemic 3/f-azepine 13.291... 

The asymmetric synthesis of / -branched carboxylic acid derivatives was accomplished by conjugate addition of mixed organoaluminum reagents to optically active Arabinose-derived c -unsaturated A-acyloxazolidinones (Scheme 47). Efficient stereocontrol was achieved using different optically active bicyclic oxazolidinones, yielding (.R)- or ( -configured / -branched carboxylic acid derivatives.136a... 

Asymmetric cyclopropanol formation has been achieved with olefmic acylsulfonamides, which act like olefmic esters. Thus, their reaction with 1 provides a method for synthesizing cyclopropanols in an optically active form. As represented by Eq. 9.41, alkylation of Oppolzer s camphor sultam and reaction of the resulting unsaturated acylsulfonamides with 1 provides optically active bicyclic cyclopropanols having exclusively the structure shown in the equation [76],... 

A parallel library of optically active bicyclic tertiary amines 127 bearing N-chiral bridgehead nitrogen atoms was readily prepared by condensation of primary amines, cyclic amino acids 126, and aldehydes. This method gives access to a large variety of substituted hexahydro-l/7-pyrrolo[l,2-/ ]imidazol-l-ones of type 127 (Scheme 16). These... 

The most reactive Michael acceptors, such as alkylidene malonates, gem-dicyanoalkenes and nitroalkenes, react with a-halozinc esters in a conjugate fashion. Beautiful examples were offered by two stereocontrolled conjugate additions to piperidinone 102 and pyrro-lidinone 104 leading to optically active bicyclic lactams 103147 (equation 60) and 105 (equation 61)148. With these electron-poor alkenes a Grignard two-step protocol is to be adopted in order to avoid the single electron transfer reactions from the metal to the Michael acceptor, which should afford olefin dimers. The best solvent is found to be a... 

During attempts to synthesize a series of optically active, bicyclic a-aminoketones (195-198), Kuneida and co-workers found that racem-ization invariably took place during the saponification and decarboxylation of the /9-ketoester intermediates, prepared via Dieckmann reactions [Eqs. (26) and (27)].253... 

In conclusion, there have been many reports of the high synthetic potential of the intramolecular aldol reaction in the enantioselective construction of cyclic enones. In particular the proline-catalyzed desymmetrization of triketones has been widely used for formation of optically active bicyclic systems which are versatile building blocks for steroids and other biologically active compounds. 

The (S)-(-)-proline catalyzed asyimietric aldol cyclization of the triketone to the optically active bicyclic aldol product, followed by dehydration to the optically active enedione, (+)-(7aS)-2,3,7,7a-tetrahydro-7a-methyl-lH-indene-l,5(6H)-dione, has been described, and two alternative reaction mechanisms have been suggested by the submitters. The exact... 

Dehydration of the optically active bicyclic ketols In refluxing benzene with a little p-toluenesulfonic acid could readily be effected without loss of optical purity.5 It has been shown by a research group at Schering A. G., Berlin, Germany that the triketone can be converted directly to the optically active enedione with 0.5 eq. of (S)-(-)-proline and 0.25 eq. of 1 N aqueous HC104 in refluxing acetonitrile.11... 

Asymmetric aldol cyclization. Complete details are available for the cyclization of the triketone 1 to the optically active bicyclic aldol product 2, first reported in 1974 (6, 411). The high asymmetric induction is attributed to formation of the rigid intermediate A by virtue of two hydrogen bonds. Other amino acids are considerably less effective for this asymmetric cyclization. ... 

Recently, Loh s indium-mediated enantioselective allylation procedure was applied by Frejd and coworkers to the synthesis of optically active bicyclic hydro-xyketones, such as (-)-endo-5, which are useful chiral building blocks in asymmetric catalysis and natural product synthesis (Scheme 4.7) [22]. 

Scheme 4.7 Synthesis of optically active bicyclic hydroxyketone 5.

This route via optically active bicyclic /-lactams has been extended to the use of the related diphenylsulfonium ethylides, allylides, and benzylides which make available highly enantiomerically enriched 1,2,3-trisubstituted cyclopropanes containing various functionalities106. 

Compound 3 is used for Robinson-typc annulation reactions yielding optically active bicyclic products such as 5. 

Optically active, bicyclic ketones were subjected to a Friedlander synthesis with 2-aminobenzaldehyde (17) to 3deld reyfo-isomeric linear or... 

HYDROPHILIC POLYAMIDE MEMBRANE PREPARED FROM OPTICALLY ACTIVE BICYCLIC OXALACTAM... 

An efficient route for the construction of chiral bicyclo[4.3.1]decanes (215) has been developed " employing an acid-catalysed intramolecular carbonyl ene reaction see (214) —> (215). Optically active bicyclic lactones have been prepared by a highly diastereo- and enantio-selective ene reaction of cyclopentenes with ethyl glyoxylate. A one-pot allylic amidation which employs the ene reaction of acylnitroso compounds (216) with electron-rich alkenes has been reported see Scheme 52. 

Scheme 4.41 Diastereoselective synthesis of optically active bicyclic a-methylene-5-...

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