Ylide 0-oxido

Carbonyls. The stereochemistry of the Wittig olefin synthesis has been reviewed. /i-a/u-Stereoselective olefin synthesis via /3-oxido-ylides is possible only in the presence of soluble lithium salts. Protonation of jS-oxido-ylides prepared from salt-free ylides leads to mixtures of erythro-and r/jr o-betaines and hence to mixtures of cis- and rm/i5-olefins. 

The jS-oxido-ylides synthesis of trisubstituted olefins has also been applied to the synthesis of farnesol (127). The phosphonium salt (123) with the aldehyde (124) and formaldehyde gave the hydroxy farnesol derivative (125) which was transformed into farnesol (127) and into (126), a position isomer of Cj juvenile hormone. 

An extension of this method can be used to prepare allylic alcohols. Instead of being protonated, the (3-oxido ylide is allowed to react with formaldehyde. The (J-oxido ylide and formaldehyde react to give, on warming, an allylic alcohol. Entry 12 is an example of this reaction. The reaction is valuable for the stereoselective synthesis of Z-allylic alcohols from aldehydes.245... 

Miscellaneous Reactions.- The Schlosser-Wittig reaction of ylide (209) with aldehyde (208) and treatment of the intermediate 6-oxido ylide with perchloryl fluoride has been used to construct the 13-fluoro unit (210) in a total synthesis of (+)-13-fluoroprosta-... 

The reaction of 1 with 2 equiv. of an aldehyde produces a tranv-allylic alcohol (3) by way of a /1-oxido ylide a (equation I). 

Unlike Wittig reagents, 1 reacts with epoxides to form a y-oxido ylide (b), which reacts with an aldehyde to form a /ran.v-homoallylic alcohol. 

A stereospecific total synthesis of prostaglandins E3 and F3, containing an additional double bond in this side chain, starts from the optically active phosphonium salt 161. In this synthesis the ( )-13-double bond and the 15-hydroxy function are generated simultaneously by condensation of the chiral bicyclic aldehyde 163 with the P-oxido ylide 162 obtained by treatment of 161 with methyllithium. The corresponding phosphonium salt S) +)-161, already possessing the (Z)-configurated A17-double bond of prostaglandins, was prepared from (S)(—)-tartaric acid 1351 (Scheme 29). 

Finally, an example of fluorination of the C = P bond has been reported." Reaction of the /1-oxido ylide 22 with gaseous perchloryl fluoride at — 35 C gives the fluoroalkenes 23A and B in 12 and 45 % yield, respectively. Alkene 23B is an intermediate in the synthesis of (-F)-13-fluoroprostaglandin methyl ester, a compound with antifertility and muscle-stimulating effects. 

Schlosser Modification. Almost pure tran -olefins are obtained from nonstabilized ylides by the Schlosser modification of the Wittig reaction (Wittig-Schlosser reaction). For example, treatment of the (cij )-oxaphosphetane intermediate A with n-BuLi or PhLi at -78 °C results in lithiation of the acidic proton adjacent to phosphoras to produce the P"Oxido phosphonium ylide B. Protonation of B with f-BuOH leads to the trans-1,2-disubstituted alkene C. 

Treatment of P-oxido ylides with electrophiles other than proton donors provides a route to stereospecific trisubstituted alkenes. For example, trapping the P-oxido phosphonium ylide B with formaldehyde (generated from paraformaldehyde) leads to dioxido phosphonium derivative D to yield, after elimination of triphenylphosphine oxide, the trisubstituted allylic alcohol... 

The stereoisomeric mixture of -hydroxyalkyl selenides resulting from the reaction of the a-selenoalkyllithium and the carbonyl compound has been often cleanly and easily separated into its constituents by liquid chromatography on silica gel (Schemes 124,133,134, and 170 172).200.206.222,226,229,258 59 jj,jg has, therefore, allowed the synthesis of each of the two stereoisomers of various di- and tri-substituted alkenes (Schemes 124,170 and 171 Scheme 172, a) and epoxides (Scheme 124 Scheme 172, b), which are otherwise obtained as intractable mixtures of stereoisomers through the conventional phosphorus or sulfur ylide methods. Last but not least, 2-lithio-2-methylselenopropane can be used as the precursor of various compounds bearing gem dimethyl substituted carbons, such as squalene, oxido-squalene, lanosterol and cholesterol. Use of commercially available perdeuterated or Ci or — 2 acetone allows the straightforward synthesis of the corresponding labelled compounds... 

Schlosser, M., Coffinet, D. a-SubstItutlon plus carbonyl olefinatlon via P-oxido phosphorus ylides (SCOOPY) reactions. Stereoselectivity of allyl alcohol synthesis via betaine ylides. Synthesis 1971, 380-381. 

Schlosser, M., Christmann, K. F., Piskala, A. Olefinatlon reactions with phosphorus ylides. II. P-Oxido phosphorus ylides in the presence and absence of soluble alkaline metal salts. Chem. Ber. 1970, 103, 2814-2820. 

In the case of the sulfur analogues, the reaction of sulfiir ylides with carbonyl compounds, known as the Corey-Chaykovsky reaction, is a well-established procedure for the synthesis of oxiranes This reaction is usually considered to involve the formation of an a/ift -betaine (205) followed by a back side attack of an oxido anion on the p-carbon. (Scheme 3.29)... 

Dauben used a related cyclization-cycloaddition approach for the synthesis of tigliane 22. Carbonyl ylide 21, derived from the diazo ketoester 20, underwent intramolecular cycloaddition to form 22, a molecule which contains the C(6), C(9)-oxido bridge of the tigliane ring system (Scheme 5) (93JOC7635). 

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