Phosphorate ylids

Horner und Winkler (115) fanden, daB das aus optisch aktivem Methyl-propyl-phenylphosphin(III) zugangliche Phosphor-Ylid I asymmetrisch mit Methyljodid reagiert. Die reduktive Spaltung der C—P-Bindung des... 

WITTIG, GEORGE (1897-1987). A University of Heidelberg professor who won the Nobel prize for chemistry in 1979 along with Herbert C. Brown of Purdue. Wittig s research showed that phosphorous ylids react with ketones and aldehydes to form alkenes. This reaction is used a great deal in the synthesis of pharmaceuticals and other complex organic substances. 

Many of the synthetic approaches that are used for the preparation of fluoroalkenes can be adopted for the synthesis of polyfluorodienes. Examples of other processes such as reductive coupling methods and syntheses based on organometallic precursors [265] or phosphorous ylids are also included in Table 7.16. 

Phosphorous ylid 0 PPhj Aldehyde, ketone Dehydration always follows... 

A related triazole synthesis utilizes phosphorous ylids, such as 264. The initially formed triazenes cyclize with elimination of triphenylphosphine oxide. The reaction proceeded sluggishly with phenyl azide, but good results have been obtained with acyl or sulphonyl azides. Tosyl azide and 264 yielded 98% of the 1-tosyl-triazole 265. The tosyl group could be removed by solvolysis in boiling ethanol... 

Wittig reaction The reaction of an aldehyde or ketone with a phosphorous ylid (also called a phosphorane), Ph3P+CR2, to give an unsaturated adduct. 

Phosphor-substituierte Pyrazolium-Verbindungen mit Phosphor-Ylid-Struktur reagieren mit Basen unter Eliminierung des Phosphor-Restes zu lH-Pyrazolen1134[s.a. Bd.El,S.781 (1982)]. 

Umsctzung des Phosphor-Ylids mit einer Carbonyl-Verbindung ... 

In the phycocyanobilin syntheses, for example, one of the two oxopyrro-methenes (46) required was prepared by a sulfur contraction route between a thiosuccinimide (44) and an a-bromomethyl pyrrole ester derivative (45a) or the corresponding phosphorous ylid (45b) (Scheme 8). Coupling of this oxopyrro-methene (46) with the formyl oxopyrromethene (47) then gave phycocyanobilin dimethyl ester (41). 

Die Organosiliciumchemie der Phosphor-ylide ist ein neuer Zweig der Ylid-Chemie, der in den letzten Jahren rasch entwickelt wurde 121 118-125), Das folgende Schema gibt eine Ubersicht iiber die beiden bisher erarbeiteten Synthesemoglichkeiten fiir die Silazanisosteren des Typs (38) ... 

Attachment to the resin allows easy isolation of the olefinic products from the phosphorous containing by-products. The reaction works well when either the carbonyl or phosphine ylid is attached to the resin. Olefins built on the solid support are usually used as resin-bound building blocks for further derivatization. [9] [10] [121] [137] [173] [243] [244] [251]... 

Deprotonierung des Phosphonium-Salzes mit einer starken Base in 2-Stellung zum Phosphor-Atom unter Bildung eines Ylids (Phosphorans) I ... 

The tetrahydroxyphosphonium cation, P(OH)J may exist in phosphoric acids and a few salts (Chapter 5.1). When a phosphonium salt has hydrogen on an a C atom, it reacts with phenyl lithium to generate a phosphonium ylid. 

Zunachst bildet sich aus dem Ylid 46 und dem Saurechlorid 139 ein Phosphoniumsalz 147. Das zweite Mol Ylid eliminiert in 147 ein Proton in y-Stellung zum Phosphor (Weg c), unter Bildung des Betains 147 (Mesomere Formen 147a und 147b) und des Phosphoniumsalzes 148. 147 zerfallt dann in das Allen 149 und Triphenylphosphinoxid. 

Die Umsetzung von 6 Mol 90 mit 1 Mol Phosphortrichlorid 300 laBt das Tri-ylid 301 entstehen. Analoge Reaktionen ergeben Phosphor-oxichlorid und -thiooxichlorid... 

Weg b Ubt R einen erheblichen —I-Effekt aus, so tritt unter Wande-rung des Protons vom a-C-Atom des Phosphors an das anionische y-C-Atom eine Michael-Addition unter Bildung des Ylids 401 ein. 

Es wird angenommen, daB sich zuerst das Betain 467 bildet, das dann in ein Phosphacydobutanderivat 468 mit funfbindigem Phosphor liber-geht, welches seineiseits in Acrylester 469 tmd das Ylid 123 zerf lt. 

In terms of its chemical reactivity, an ylid such as 126 may be viewed as a phosphorus-stabilized carbanion that will undergo acyl addition with an aldehyde or a ketone. When this ylid is mixed with cyclohexanone (80), there are two isolated products. The one that is more interesting to an organic chemist is methylenecyclohexane (129), formed in 52% yield the other is tri-phenylphosphine oxide, 130. It is obvious that 129 is not the expected acyl addition product. Formation of 130 indicates that the carbon atom of the ylid has been transferred to the ketone, but the oxygen atom of the ketone has been transferred to the phosphorous atom. Analysis of the reaction shows that the oxygen atom is lost from the ketone, and the CH2 unit of ylid 126 is transferred to form a new C=C bond (in green in the illustration). What is the mechanism ... 

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