Olefinations, synthesis

So the FGI stage in designing an olefin synthesis is to add water across the double bond. How would you synthesise TM 36 ... 

Olefin synthesis starts usually from carbonyl compounds and carbanions with relatively electropositive, redox-active substituents mostly containing phosphorus, sulfur, or silicon. The carbanions add to the carbonyl group and the oxy anion attacks the oxidizable atom Y in-tramolecularly. The oxide Y—O" is then eliminated and a new C—C bond is formed. Such reactions take place because the formation of a Y—0 bond is thermodynamically favored and because Y is able to expand its coordination sphere and to raise its oxidation number. 

Low-valent nitrogen and phosphorus compounds are used to remove hetero atoms from organic compounds. Important examples are the Wolff-Kishner type reduction of ketones to hydrocarbons (R.L. Augustine, 1968 D. Todd, 1948 R.O. Hutchins, 1973B) and Barton s olefin synthesis (p. 35) both using hydrazine derivatives. 

BARTON KELLOGG Olefinalion Olefin synthesis (letrasubsirtuted) from hydrazones and thiokelones via A -f,3,4-Ihiadiazollnes. 

Hydroboration - regloseiective and stereoselective (syn) addition of BH3 (RBH2, R2BH) to olefins. Synthesis of alcohol including optically active alcohols from olefins. Also useful In synthesis of ketones by stitching ot olefins and CO... 

COPE - MAMLOC - WOLFENSTEIN Olefin synthesis Olefin formalion by elimination from tert amine N-oxides... 

GAREGG - SAMUELSSON Olefin Synthesis Conversion of vie Irans-dwl groups into a double bond by lodine-lnphenylphosphine-imidazole reagent. 

PAQUETTE Olefin Synthesis OesuHonatlon of suHones to alkenes (altemative to Ramberg-Backlund). 

RAMBERG BACKLUND Olefin Synthesis Conversion of dialkyl suNones to akenes by rearra/tgement of a-haiosulfones with base (via imaranedloxfdes). 

Olefin synthesis Irom phosphorane ylides (e g 3) with aldehydes or ketones cis olelins predominate in aliphatic systems trans m coniugated olefins... 

Julia and Paris120 described an olefin synthesis, based on the use of a sulphonyl group which directs the formation of a carbon-carbon bond. Subsequent reductive elimination with sodium amalgam leads to the alkene, as outlined in equation (50). The reaction sequence is similar in principle to an olefin synthesis first developed by Cornforth121. The yields of all steps are generally above 80%. 

A second paper161 describes the use of the same base in either THF or t-butanol for the elimination of a-acetoxy phenyl sulphones as outlined in equation (68), in essence a reaction sequence very similar to the Julia olefin synthesis (Section III.B.3) except in the method by which the sulphonyl group is finally removed. 

Taft s Terminal olefins, synthesis of 629 Tertiary alcohols, allylic, epimerization of 736... 

A. Preparation.—The first reverse Wittig olefin synthesis has been reported. Triphenylphosphine oxide and dicyanoacetylene at 160 °C gave the stable ylide (1 78%) the reaction was reversed at 300 °C. No comparable reaction was observed with a variety of other activated acetylenes but tri phenyl arsine oxide gave the corresponding stable arsoranes with dicyanoacetylene (— 70 °C), methyl propiolate, hexafluorobut-2-yne, dimethyl acetylene dicarboxylate, and ethyl phenylpropiolate (130 °C). 

Phosphonium fluorides have been used in olefin synthesis without additional base, the fluoride anion being sufficiently strong a base to remove the ct-proton from the salts (2 R = Ar or COR ) in acetonitrile. 

B. Reactions.—(/) Halides. Whereas ylides are alkylated in the normal way on treatment with a-bromo- or a-iodo-esters, quite different reactions occur with a-fluoro- and a-chloro-acetates. When salt-free ylides were refluxed in benzene with ethyl fluoroacetate or trifluoroacetate normal Wittig olefin synthesis took place with the carbonyls of the ester groups to give vinyl ethers, e.g. (14). On the other hand, methyl chloroacetate with... 

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 quality of phenyl-lithium used to generate ylides can have a pronounced effect on the stereochemistry of olefin synthesis. In the reactions of the ylide (36) with the aldehydes (37) c/5-olefins were obtained using a phenyl-lithium solution containing one equivalent of total base while /m/ij-olefins resulted from the use of an amount of this solution containing one equivalent of genuine phenyl-lithium together with six equivalents of other, unspecified, base. ... 

A polymer containing side-chain benzylphosphonium residues has been prepared and used in olefin synthesis. A suspension in THF was treated with base and benzaldehyde overnight and the polymeric phosphine oxide was then removed by filtration. The yields of stilbenes, 40% with potassium t-butoxide and 60% with sodium hydride, were not improved by using an excess of base or of aldehyde. 

The formation of the naphthalene (73) from the bis-ylide (72) and diethyl ketomalonate involves an unusual olefin synthesis on the carbonyl of an ester group. The methylene-pyrans (75) were formed when the diethyl malonates (74) were refluxed with j3-keto-ylides in xylene or decalin. Possible intermediates are the ketens (76) and the allenes (77). Addition of ylide to the allenes gives the betaines (78) which form methylene-pyrans either directly or via acetylenes as shown. 

The reaction between benzylidenetriphenylphosphorane and benzonitrile has been reinvestigated and the primary product (82) isolated. Stable ylides react similarly with activated nitriles, e.g. cyanogen and trifluoro-acetonitrile, but cyanomethylenetriphenylphosphorane with methyl cyano-formate gave largely the vinyl ether (83), the product of a normal olefin synthesis on the carbonyl of the ester group. 

A normal olefin synthesis took place between a carbonyl ligand of bromopentacarbonylmanganese and hexaphenylcarbodiphosphorane to give an organometallic ylide. 

Zeaxanthin (135) was synthesized from the salt (133) and the dialdehyde (134) in 1,2-epoxybutane, a reagent superior to ethylene oxide particularly for polyenedialdehydes. The same salt was also used to prepare /3-cryptoxanthin and zeinoxanthin. Phenolic carotenoids from Strep-tomyces mediolani and 1,2-dihydro- and l,2,r,2 -tetrahydro-lycopene have also been obtained by conventional olefin synthesis. 

C. Miscellaneous.—Among ylides, PhsP CHR, used in conventional olefin synthesis with protected keto-sugars are those with R = H, CN, SMe, and COR. ... 

A study of the decomposition in basic media of the erythro- and threo-isomers of the /8-hydroxyphosphonate (169) showed that the first step in the phosphonate olefin synthesis is reversible and that the diastereo-isomers of (169) can also interconvert directly, presumably via the a-car-banion. 

Among phosphonate esters (170) used in olefin synthesis were those with R = S-CeHi-Br-/ , S02 C6H4-Br-A CO-NHR, and S CHa CEi-XHa. The allyl vinyl thio-ethers (171) obtained using the last of these gave a-allyl-aldehydes on pyrolysis in the presence of red mercuric oxide. 

Corey s phosphonamide olefin synthesis has been extended to the synthesis of vinyl ethers using the phosphonamides (Me2N)2P( O)- CHjOR. 

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