Seleno esters synthesis

Seleno esters are also produced in good yield by reactions of dimethy-laluminim methanoselenolate103 (CH3)2AlSeCH3, with the protected C-ribofuranosyl acetate 269. Treating the selenol ester 270 with either cuprous or mercuric chloride produced the (Gensler) lactone.110 271, a product useful in the synthesis of various C-nucleoside antibiotics.111,112... 

The formal total synthesis of the selective muscarinic receptor antagonist (+)-himbacine was accomplished by M.S. Sherburn and co-workers using an intramoiecuiar Dieis-Aider reaction, a Stiiie cross-coupling, and a 6-exo-trig acyi radical cyclization as the key steps.In order to prepare the selenoate ester precursor for the radical cyclization step, the aldehyde-enyne substrate was converted to the carboxylic acid via the Pinnick oxidation without affecting the delicate enyne moiety. 

Recently, Pattenden, following the same D strategy, has developed the use of a-ketenyl cyclooctanyl radical 114 toward a new and concise formal synthesis of modhephene (Scheme 33). The (x,)5-unsaturated seleno ester 112, treated under usual BusSnH-AIBN conditions, generates the corresponding a,/9-unsaturated acyl radical 113, which transannularly cyclizes via its mesomeric radical counterpart 114. The resulting tertiary radical undergoes a 5-cxo-dig cyclization onto the ketene central carbon giving rise to a final enoxy radical, which is reduced to provide the tricyclic ketone 115 [49]. 

Over the last decade there has been great interest in the synthesis and use of 2- and 3-indolylacyl radicals generated from seleno esters and glyoxylic acids, fuelled by the work of Beimasar [22]. Early reports from this group outlined the intermo-lecular addition reaction of such generated radicals to various alkenes and pyridines [23, 24]. 

Azocino[3,2-6]indoles were obtained when seleno ester precursors bearing 3-butenylamino and allylaminomethyl chains on the C-3 position of the indole were subjected to the same reductive radical conditions used previously with indole 237. Inclusion of a bromine atom on the alkene acceptor gave the most rewarding result (shown below) at a hydride concentration of 0.02 M yielding 75% of the %-endo product 241, without the detection of any products, formed as a result of reductirm or the alternative 1-exo cyclization. This method proved to be a nice complement to the ring-closing metathesis protocol used in this laboratory to effect similar cyclizations and recently resulted in the total synthesis of apparicine [126, 127]. 

Renaud and co-workers used 78 for the synthesis of (-)-phaseolinic acid (6) and (-)-pertusarinic acid (8) (Scheme 12) [32, 33]. Radical addition of dimethyl phenylselenomalonate to 78 proceeded with rearrangement of the bicyclics to yield the seleno-acetal 79 [34]. After reductive deselenylation and Baeyer-Villiger oxidation treatment of 80 with BU4NI and BBr3 led to a simultaneous cleavage of the ether, the lactone, and the methyl ester func-... 

Yamazaki, S., Imanishi, T., Moriguchi, Y, and Takada, T., Highly efficient 2 -t- 1] cycloaddition reactions of a l-seleno-2-silylethene to 2-phosphonoacrylates. Synthesis of novel functionahzed cyclo-propanephosphonic acid esters. Tetrahedron Lett., 38, 6397, 1997. 

Synthesis of Phosphoric Acids and Their Derivatives. - A series of monoalkyl and dialkyl phosphorus acid chiral esters have been synthesised for use as carriers for the transport of aromatic amino acids through supported liquid membranes. The compounds acted as effective carriers but enantio-separation was at best moderate. A range of phosphono- and phosphoro-fluoridates have been prepared by treatment of the corresponding thio- or seleno- phosphorus acids with aqueous silver fluoride at room temperature (Scheme 1). In some cases oxidation rather than fluorination occurred. Stereospecifically deuterium-labelled allylic isoprenoid diphosphates, e.g. (1), have been synthesised from the corresponding deuterium-labelled aldehyde by asymmetric reduction, phosphorylation and Sn2 displacement with pyrophosphate (Scheme 2). ... 

The synthesis of phosphonic acid derivatives by the direct oxidation of those of the corresponding phosphonous acid has been afforded very little interest (Chapter 2, Section VI.c), unlike the more controllable synthesis of derivatives of the thio- or seleno-phos-phonic acid derivatives (Chapter 5, Section II.B.4). In the present instance, the oxidation of A -protected (fmoc) (l-aminoalkyl)phosphinic esters has been carried out with NaI04 with high yields. Quantitative yields of (aminoalkyl)phosphonic acids were obtained in oxidation reactions with bromine water and with HgCl2-H20. In an alternative approach (Scheme 59), the A -protected (cbz) ethyl(l-aminoalkyl)phosphinate is initially converted into a (l-aminoalkyl)phosphonous acid diester, which is then subjected to the Atherton procedure to achieve change in valence at phosphorus. ... 

The only comprehensive and readily-available surveys of thio- and seleno-phosphonic and -phosphinic acids appear to be those in the compilation by Kosolapoff and Maier which appeared during the 1970s, and those in the Houben-Weyl volumes. Some further information relevant to heterocyclic systems which possess endo- or exo-cyclic phosphorus-sulphur bonds has been surveyed by Mann Gefter has also provided a useful compilation of syntheses and data for unsaturated thiophosphonates and related compounds. As in the preceding chapters concerned with the synthesis of the various classes of phosphonic and phosphinic acids, literature surveys have been presented for individual compounds and the field, as a whole, is surveyed annually". In addition. Hall and Inch reviewed the mechanistic implications of changes in stereochemistry following displacement reactions at phosphorus in cyclic phosphorus(V) esters and amides, and in so doing discussed the reaction s of many such thiophosphoryl compounds. 

The synthesis of naturally occurring A-acetylneuraminic acid (912) utilizes the chirality of D-lactate (898) to set the stereochemistry of hetero Diels-Alder adduct 910 [247] (Scheme 121). The dienophile, ( S)-seleno aldehyde 908, is prepared by inversion of mesylate 906 followed by controlled reduction of the ester with diisobutylaluminum hydride at low tern-... 

Abstract This chapter reviews studies into the preparation of thio-, seleno-, and telluro-car-boxylic acid esters (referred to thiol, selenol, and tellurol esters, respectively) and into their use in organic synthesis. The studies reviewed here span the last ten years, although some important and original findings reported further back than this are also included. 

Seleno-carboxylic acid esters (selenol esters) 2 are also prepared like thiol esters by the reaction of acyl halides with selenols, or diselenides as well as their alkali metal salts. Most of the preparative methods for thiol esters shown in Sect. 2.1 are applicable to the synthesis of selenol esters 2. Unique synthetic... 

By using the a-fluoro a-seleno-substituted ester 45b prepared in this fashion, a highly stereoselective synthesis of a-fluoro a,P-unsatu-rated ester 48 was achieved, as shown in Scheme 37. Substances of this type are useful for the preparation of monofluorinated retinoids, insect sex pheromones, and pyrethroids. ... 

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