Wittig methodology

A variety of routes are available for the preparation of allylsilanes (/) with the simplest and most direct being the silylation of allyl-metal species. Other routes exemplified in this chapter include Wittig methodology, the use of silyl anions/anionoids in allylic substitution, and hydrometallation of... 

Previous syntheses of terminal alkynes from aldehydes employed Wittig methodology with phosphonium ylides and phosphonates. 6 7 The DuPont procedure circumvents the use of phosphorus compounds by using lithiated dichloromethane as the source of the terminal carbon. The intermediate lithioalkyne 4 can be quenched with water to provide the terminal alkyne or with various electrophiles, as in the present case, to yield propargylic alcohols, alkynylsilanes, or internal alkynes. Enantioenriched terminal alkynylcarbinols can also be prepared from allylic alcohols by Sharpless epoxidation and subsequent basic elimination of the derived chloro- or bromomethyl epoxide (eq 5). A related method entails Sharpless asymmetric dihydroxylation of an allylic chloride and base treatment of the acetonide derivative.8 In these approaches the product and starting material contain the same number of carbons. 

In the construction of C=N bond-containing compounds, such as nitrogen heterocycles, the aza-Wittig methodology has received increased attention as the method of choice [7]. Thus, an easy access to optically active (-)-vasicinone (7-15), a pyr-rolo[2,l-fc]quinazoline alkaloid which is used in indigenous medicine [8], was... 

A new approach to anisomycin from D-erythrose using Wittig methodology is outlined. 

Our initial work involved the synthesis of side chains which have the molecular characteristics required for a nonlinear optical response. Compounds 1-3 were prepared by the use of Horner-Emmons-Wadsworth Wittig methodology (22). Compound 4 was commercially available (Aldrich) as the dye, Disperse Red 1. As outlined in Scheme I, in the first step in the synthesis of 1-3,... 

What variation in the Wittig methodology is also often used to synthesize E olefins ... 

Wittig methodology has been used to prepare a variety of heterocyclic species, including cyclopentenones and cyclohexenones through the intramolecular Wittig reaction of 2-oxoalkylidenetriphenylphosphoranes (52) (Scheme 14), fluor-inated butanolides and butenolides, 2,5-disubstituted-pyrroles and -pyr-rolidenes, which utilised the phosphorane 4-[ 4-methylphenyl)sulfonyl]-l-... 

Early synthetically oriented divinylcyclopropane-cycloheptadiene rearrangements were performed with hydrocarbons and were in part due to the interest in syntheses of marine brown algae constituents. The preparation of ectocarpene is displayed in equation 164. The corresponding divinylcyclopropanes have either been constructed by Wittig methodology or, as in the case shown, by addition of diazoalkanes to apt polyenes followed by photolysis or thermolysis . 

Because Michael-type reactions are among the most useful base-mediated cyclizations, the first examples presented in this chapter center around this chemistry. Thus, utilizing Wittig methodology, Vyplel et al. [37] prepared the hydroxyolefin (shown in Scheme 7.93) from the starting protected glucosamine. Treatment of this intermediate species with DBU effected cyclization of the 5-hydroxy group to the unsaturated ester in a Michael fashion. Notably, the cyclization provided the a anomer in 43% yield, with an additional 7% accounted for in the isolation of the (3 anomer. 

Eguchi, S., Okano, T., Okawa, T. Synthesis of heterocyclic natural products and related heterocycles by the aza-Wittig methodology. Rec. Res. Dev. Org. Chem. 1997, 1, 337-346. 

The (S )-acid (40) was also prepared [70] starting from the commercially available chiral building block ( S)-methyl 3-hydroxy-2-methylpropionate, which was transformed into the same intermediate alcohol (41) and finally submitted to a Wittig methodology (Scheme 23). 

Alternatively, Wittig methodology has been invoked for the synthesis of... 

We chemically synthesized 3M2H using the Wittig methodology (see Pierce, Jr. et al., 1996 for the protocol). Heterosexual female volunteers (aged 18-40), who did not use oral contraceptives, served as the subjects. Participants were asked to fill out a form to... 

MBH adduct 842 has subjected to epoxidation with m-CPBA followed by a Swern oxidation to afford aldehyde 844 (Scheme 4.244). Wittig methodology using (iodomethylene)triphenylphosphorane gave iodide 845 in 34% overall yield. Iodide 845 was subsequently treated with sodium benzylselenoate to afford 846 and then free-radical mediated ring closure as well as ester hydrolysis afforded selenophene-3-carboxylic acid 847 in 26% yield within two steps. Acid... 

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