Wittig strategy

As Scheme 97 shows, employing macrocyclic lactams 263 and o-azidoben-zoyl chloride, 4(3//)-quinazolinones (264) are obtained with the aid of an aza-Wittig strategy. Reductive cleavage of the C-2 —N-3 bond of quinazo-... 

An enantioselective aza-Wittig strategy has been employed in the desymmetrization of prochiral 1,3-diketoazides, to produce /3-quaternary azacycles.241... 

The optical brightener Palanil 50—it makes your clothes look whiter than white and your T-shirts fluoresce in UV light—can be disconnected by the Wittig strategy to two molecules of the phosphonium ylid 51 and one of the dialdehyde 52. The availability of the dialdehyde, used in the manufacture of terylene, makes this route preferable to the alternative. 

In this synthesis (Scheme 6), the C2-symmetri-cal triacetonide of D-mannitol (32) is converted via the epoxide 33 and its nucleophilic addition product 34 to the propargylic alcohol derivative 35. From this intermediate, the Z-configured vinyl iodide 36 is stereoselectively obtained by hydroalumination/iodination. The Pd-catalyzed Heck cyclization then affords the isomerically pure product 37, which represents a potential building block for the synthesis of la,2y5,25-trihy-droxy-vitamin D, following the classical Wittig strategy of Lythgoe. 

Woodward s Wittig strategy was also applied to the preparation of aza-p-lactams [36]. Thus A -aza-cephem 59 was obtained in satisfactory yield by this method (Scheme 19). However this compound could not be isomerised into... 

Flavonoids are a class of widely distributed naturally occurring phenolic compounds, the most abundant being the flavones. Members of this class display a wide variety of phannacological activities and have been useful in the treatment of various diseases. Flavones have been prepared by a variety of methods such as Allan-Robinson synthesis and synthesis from hydroxychalcones via an intramolecular Wittig strategy. The most popular approach, however, involves the Baker-... 

In the last example, a more direct approach to make the vinyl group may be via a Wittig strategy from a nicotinic aldehyde or via a direct aromatic substitution strategy. It should be noted that the Wittig and Heck reactions were known at the time the Merck, Gates, and Martin plans of quinine were disclosed. 

Numerous research papers and several reviews have appeared describing the general use of phosphazenes as reagents and intermediates in organic synthesis. This account describes the use of the aza-Wittig reaction for the preparation of natural products by means of intermolecular and intramolecular processes. Despite the aza-Wittig strategy... 

On the other hand a convenient combination of intramolecular aza-Wittig strategy and microwave technology for the preparation of the alkaloid, cryptotackieine, which has an indolo[2,3-h]quinoline core, has been described. Thus, treatment of 3-(o-azidophenyl) quinolin-2-one 145 with trimethylphosphine in nitrobenzene under microwave irradiation between 150-180 °C, after five-membered ring construction, afforded cryptotackieine (51) in 40% yield via 146 (Scheme 15.33). 

More recently, P-cored derivative (116) was prepared from a straightforward combination of a Heck coupling, to afford an intermediate functionalised stil-bene phosphine oxide (114),a Horner-Wittig reaction yielding the phosphine oxide (115), and finally trichlorosilane reduction (Scheme 31) [89]. Using similar strategies, both the valence isoelectronic N- (117) and C- (118) cored dendrimers have been prepared (Scheme 31). 

Ipomeamarone has been synthesised by a slight variant on this strategy in which the methyl group is added to lactone (47) and a Wittig reagent is used for synthon (42) ... 

Annulation of pyridine to indole is accomplished by a tandem aza-Wittig/electrocyclization strategy as shown in Eq. 10.68."... 

In one example of application of the RCM strategy, summarized in Scheme 107, the key intermediate 454 was obtained from 451 by sequential Wittig methylenation to 452, reductive iV-deprotection to 453, and introduction of an alkenyl chain onto the secondary amine. The RCM reaction of 454 to 455 proceeded in quantitative yield in the presence of the second-generation Grubbs catalyst <20040L965>. 

In order to establish the correct absolute stereochemistry in cyclopentanoid 123 (Scheme 10.11), a chirality transfer strategy was employed with aldehyde 117, obtained from (S)-(-)-limonene (Scheme 10.11). A modified procedure for the conversion of (S)-(-)-limonene to cyclopentene 117 (58 % from limonene) was used [58], and aldehyde 117 was reduced with diisobutylaluminium hydride (DIBAL) (quant.) and alkylated to provide tributylstannane ether 118. This compound underwent a Still-Wittig rearrangement upon treatment with n-butyl lithium (n-BuLi) to yield 119 (75 %, two steps) [59]. The extent to which the chirality transfer was successful was deemed quantitative on the basis of conversion of alcohol 119 to its (+)-(9-methyI mande I ic acid ester and subsequent analysis of optical purity. The ozonolysis (70 %) of 119, protection of the free alcohol as the silyl ether (85 %), and reduction of the ketone with DIBAL (quant.) gave alcohol 120. Elimination of the alcohol in 120 with phosphorus oxychloride-pyridine... 

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