Isopropylidene phosphorane

Mori also succeeded in synthesizing the optically active ipsdienol 350 via carbonyl olefination of the acetonide 345 of (RX+)-glycerine aldehyde with isopropylidene-phosphorane to form 346. Methoxymercuration of346 followed by the splitting of the protective group, tosylation and treatment with alkali afford the epoxide 349 which is converted into the optically active (R)-350 via the same reaction sequence as in the synthesis of 344 according to Scheme 61 2101 (Scheme 62). 

Vilsmeier reaction to the chloroaldehyde (106), followed by reductive meth-ylation, yielded the aldehyde 107 (Scheme 14) with the precedented stereochemical outcome. Attempted halogenation of the derived neopentyl-type alcohol was unsuccessful under a variety of conditions, so an alternative scheme involving two successive Wittig-type reactions was developed. The aldehyde 107 was converted to the unsaturated aldehyde 108 by the method of Nagata and Hayase. Reduction with triethylsilane and tris (triphenylphosphine) rhodium chloride was followed by condensation with isopropylidene phosphorane to give the desired product 109. 

The introduction of the phosphonate grouping into a sugar molecule (see Section III, 3 p. 260) has been further investigated by Paulsen and coworkers.97 Thus, the phosphonate phosphorane 120a was shown to react with 2,3,4,5,6-penta-O-acetyl-a/dehydo-D-glucose, 2,3 4,5-di-0- isopropylidene - aldehydo - D - arabinose, and 2,4-0-ethylidene-a/dehi/do-D-erythrose, leading to the unsaturated phos-phonates 229, 230a, and 231, respectively, in moderate yields. 

Enantioselective cyclopropanation. The reaction of dimenthyl fumarates (2) with isopropylidene(triphenyl)phosphorane proceeds in 74% de in THF at -78 — 20°. (1S,3S)-3 is obtained when the /-menthyl group is used inductor (lR,3R)-3 is obtained in the same optical yield when the unnatural //-menthyl group is used. The concentration plays an important role enantioselectivity is increased by dilution and decreased by concentration. 

E19b, 108 (Carben + En) (1-Ethyl-pentyliden)- E17b, 1678 (Phosphoran + H5C2-CO-C4H9) 1-Isopropyliden-tetramethyl- El7b, 1118 (subst. 4,5-H2 — 3H-pyrazol/ hv or A) E19b, 107/113/115 (Carben + En)... 

Phosphoran (Bis-[trimethylsilyl]-amino)-isopropyliden-(trimethyl-silylimino)- El, 599 [(R3Si)2N-P=N-SiR3 + S8]... 

Synthesis from o-mannose A total synthesis of D-(- -)-biotin (1) from D-mannose has also been reported (Scheme Treatment of 2,3 5,6-di-0-isopropylidene-a-D-mannofuranose (17) with benzoyl chloride followed by selective hydrolysis of the terminal acetal group afforded 1-0-benzoyl-2,3-0-isopropylidene-a-D-mannofuranose (18). Subsequent periodate oxidation and chain extension with the proper phosphorane followed by hydrogenation gave the uronate derivative 19. Treatment of 19 with NaOCHs followed by reduction of the resulting aldehyde with sodium borohydride afforded compound 20. 

The dione (100) reacted exclusively at the exocyclic carbonyl in a synthesis of methyl 9-cis- (101) and 9-rra/i5 -trisporates B. Although ( )-dihydro-j8-santalol (103) was obtained from (102) in 90% yield if the hydroxy-group was protected as the borate ester, use of unprotected (102) gave predominantly the isomeric olefin (104). Similarly the hydroxy-ketone (105) gave the olefin (106), but similar rearrangements did not occur using the isopropylidene- or ethoxycarbonylmethylene-phosphoranes. 

Carbohydrate-based phosphoranes were synthesized by reacting the appropriate diphenol with phosphorus trichloride followed by the addition of chloralose to form (60) and by the addition of isopropylidene-D-glucofuranose to form (61) and (62) in the presence of A -chlorodiiospropylamine. 

Reaction of 3-acetamido-3-deoxy-4,5 6,7-di-0-isopropylidene-2-0-methyl-a/dle/i> dlo-D-g/yccro-D-gfl/flcro-heptose with [ethoxy(ethoxycarbonyl)methylene]-triphenyl-phosphorane, followed by an ethoxymercuration-demercuration reaction and acid hydrolysis resulted in the formation of the ethyl esters of 4-0-methyl-N-acetylneuraminic acid and 4-0-methyl-4-epi-N-acetylneuraminic acid (Beau et al. 1978). By oxymercuration of ethyl 5-acetamido-3,5-dideoxy-2-0-ethyl-4-0-methyl-D-g/jcero-D-ga/acto-non-2-enonate with mercury(II) trifluoroacetate, followed by borohydride-demercuration, 4-0-methyl-N-acetylneuraminic acid ethyl (3-glycoside was obtained (Beau et al. 1980). 4-0-Methyl-N-acetylneuraminic acid has been used in metabolism studies, as reported by Beau and Schauer (1980). Using tritiated sodiumborohydride, the corresponding 4-0-methyl-N-acetyl-[3-3H]neuraminic acid was obtained (Beau and Schauer 1980). 

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