Isopropylidene triphenylphosphorane

As a further Wittig synthon isopropylidene-triphenylphosphorane was used for the preparation of trans 2,6-famesol and trans-nerolidol 236) which are structurally related to one another like linalool and geraniol. 

Preparatively important is the reaction of isopropylidene triphenylphosphorane which provides gem-dimethyl-substituted cyclopropanes. In general, the E configuration of the precursor alkenes is retained to give the /ra/w-substituted cyclopropanes 618 20. 

A similar desire for geminal dimethyl-substituted cyclopropanes resulted in the use of isopropylidene triphenylphosphorane as the carbene source. Reaction with acceptor-substituted alkenes carrying inducing auxiliaries gave intermediates for syntheses of chrysanthemic acid derivatives. Thus, the addition to (A )-butencdioatcs provides 3,3-dimethyl-1,2-cyclopropanedi-earboxylates 3986. The highest diastereoselectivity is observed with the (—)-8-phenylmenthyl derivative which gives the cyclopropane with a d.r. of 91 9. 

Methyl (R)-/rara-4,5-0-isopropylidene-4,5-dihydroxy-2-pentenoate and isopropylidene triphenylphosphorane furnish the (l/ ,2/ )-tra .s-cyclopropane derivative 40 as the major diastereomer (d.r. 93 7) with a 60% yield87. Starting with the corresponding ethyl ester, a d.r. of >98 2 can be obtained. Purification of these intermediates by recrystallization, followed by oxidative degradation of the inducing dioxolane moiety, leads to methyl (/ ,/ )-2-formyl-3,3-dimethylcy-clopropanecarboxylate [(lR.2/ )-hemicaronic aldehyde] in enantiomerically pure form. 

When isopropylidene triphenylphosphorane is added to the (1 /(.2,S)-norephcdrinc based unsaturated oxazolidine 41 the cyclopropane derivative is formed as a single diastereomer in 60% yield88. Removal of the heterocyclic auxiliary affords optically pure methyl (R,R)-2-formyl-3,3-dimethylcyclopropanecarboxylate [(1 / ,2/ )-hemicaronic aldehyde, 42],... 

Aus dem Isopropyliden-triphenylphosphoran 150 und Acetylchlorid 151 bildet sich bei Raumtemperatur neben dem Salz 153 das isolierbare Betain 152. 

Setzt man das Isopropyliden-triphenylphosphoran 419 mit Crotonsaure-methylester 421 um, so erhalt man nur das Cyclopropanderivat 416. Die all-cis-Verbindung, in der zwei Methylgruppen und die Estergruppe auf... 

Ready access to 2-C-D-ribofuranosylacetates can be gained from the reaction of 2,3-O-isopropylidene-D-ribofuranose (186) with (eth-oxycarbonylmethylene)triphenylphosphorane in boiling toluene.137 The reaction proceeds with remarkable stereocontrol, to give crystalline ethyl 2-C-(2,3-0-isopropylidene-/3-D-ribofuranosyl)acetate... 

Di-0-isopropylidene-a-D-rtbo-hexofuranos-3-ulose (100) was treated with (chlorofluoromethylene)triphenylphosphorane (prepared by reaction of triphenylphosphine on difluorocarbene generated in situ by reaction of potassium ferf-butoxide with dichloro-fluoromethane), to give cis- and rans-3-C-(chlorofluoromethylene)-3-deoxy-l,2 5,6-di-0-isopropylidene-a-D-ribo- (101 and 103) and -xyfo-hexofuranoses (105 and 107), which, on treatment with lithium aluminum hydride, gave cis- and frans-3-deoxy-3-C-(fluoromethyl)-1,2 5,6-di-O-isopropylidene-a-D-rtbo- (102 and 104) and -xyZo-hexofura-... 

The diversity associated with silyl protecting groups as well as the chemical conditions available for their removal makes them attractive alternatives to benzyl protection of the hydroxy groups of either D- or L-tartaric acid derivatives. O-isopropylidene-L-threitol (37) is mono-protected with er -butyldimethylsilyl chloride to furnish 266, which is converted in three steps to the nitrile 267. Reduction with DIBAL and Wittig olefination followed by desilylation with fluoride and Swern oxidation of the resulting alcohol provides aldehyde 268, which reacts with methyl 10-(triphenylphosphorane)-9-oxo-decanoate (269) to afford enone 270. Reduction of 270 with subsequent preparative TLC and acetal hydrolysis furnishes (9R)-271 and (9 S)-272, both interesting unsaturated trihydroxy Cig fatty acid metabolites isolated from vegetables [91] (Scheme 62). 

Reaction of enal 118, obtained by formylmethylene triphenylphosphorane treatment of 2,3-0-isopropylidene-D-glyceraldehyde with the Vedejs reagent 119... 

A soln. of 2,3-0-isopropylidene-5-0-trityl-D-ribofuranose and (ethoxycarbonyl-methylene)triphenylphosphorane in dry acetonitrile refluxed 6 hrs., cooled to room temp., if two sugar spots are present solid K-/ rt-butoxide added, and stirred at room temp, until TLC indicates their disappearance crude ethyl 2-(2,3-0-isopropylidene-5-0-trityl-D-ribofuranosyl)acetate. Y 90%. C. K. Chu et al., J. Org. Chem. 41, 2793 (1976). 

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