Tandem Wittig reaction

Naturally occurring 6-prenylcoumarins have been synthesised from 2-prenyloxy-benzaldehydes through tandem Wittig reaction and Claisen rearrangement. Several of the... 

M4604>. The synthesis of a fullerene embedded with a furan motif was reported, which was confirmed by a single crystal X-ray analysis <07OL1741>. Tandem Wittig reaction-intramolecular Diels-Alder cycloaddition of 2-furfural provided tricyclic furans, which may serve as precursors in the synthesis of furanosesquiterpenes <07TL3517>. 

A new route to 2-(52) and 3-(51)-(2-aminovinyl)indoles in excellent yield is provided by the reaction of 2- and 3-acylindoles with the carbanions of 1-aminoalkyldiphenylphosphine oxides (50) (Scheme 7).29 The previously established method of diene synthesis using tandem Wittig reactions of the phospholanium salt (53) has been applied to the synthesis of the sex pheromone (54) from the pedal gland of the bontebok (Damaliscus dorcas dorcas) and to various 1,4-diketones (Scheme 8).30... 

Reactions at C-2 of V-protected indoxyls provide entry to novel indoles that are difficult to access other ways. Sakamoto and colleagues discovered a tandem Wittig reaction and Cope (or Claisen) rearranganent to provide... 

In 2004, Whittlesey and Williams demonstrated that the reversible C-H activation of Ru-NHC complexes (e.g. 32a, Scheme 13.14) provides an effective manifold for tandem dehydrogenation/Wittig reaction/hydrogenation of alcohols, thus generating alkanes from alcohols and phosphorus ylides [56]. 

Scheme 13.15 Tandem Borrowing Hydrogen Wittig reaction with Ru-NHC complexes...

Finally, the synthesis of 4//-3,l-benzoxazines 239 via a tandem aza-Wittig reaction (Scheme 89) should be mentioned. Carbodiimide 238 or isocyanate generated by an intramolecular aza-Wittig reaction bears an o-hydroxymethyl group on the A(-aryl substituent this OH attacks the carbodiimide C intramolecularly with cyclization to give a 3,1-benzoxazine (91S21). 

Via tandem Michael-type addition followed by an aza-Wittig reaction, 2,3,6,7-tetrahydro- and 2,3,4,5,6,7-hexahydro-lH-l,4-diazepines have... 

A unique tandem Staudinger-Wittig reaction finds application in lactam synthesis ... 

Similar results were observed by Davies and McKervey in the tandem Mn02 oxidation-Wittig reaction of alcohols derived from (3-aminoacids, which can somehow be considered to belong to a semi-activated kind.30... 

It is important to note that this tandem Mn02 oxidation-Wittig reaction is particularly useful when the intermediate aldehydes are difficult to isolate. For example, it allows successful Wittig reactions on a-ketoaldehydes,61e which are compounds inconvenient to isolate because of their very high reactivity. 

In this example, a successful tandem Mn02 oxidation-Wittig reaction is achieved, using a non-stabilized ylide, thanks to the employment of pre-dried Mn02, the guanidine (78) as... 

Scheme 9 Proposed mechanism and substrate scope for tandem alcohol oxidation/Wittig reaction/alkene hydrogenation sequence...

This C - H activation event is reversible, and is required to achieve catalytic turnover [62], A series of alcohols, mostly secondary benzylic examples, have been oxidized using this catalyst. The catalytic activity does not match that of the Ir examples described above, but it has been used in several tandem reactions that feature both dehydrogenation and hydrogenation steps to achieve interesting transformations. One example is a tandem alcohol oxidation/Wittig reaction/alkene hydrogenation sequence (Scheme 9) [61,62],... 

Cycloalkenes by tandem addition-Wittig reactions of vinylphosphonium salts... 

The tandem Wittig-conjugate-addition reaction shown below has found widespread application for the synthesis of C-nucleosides from aldoses, in most cases ribose (see also Section 4.7.1.2.2. for the related reaction of aldoses with nitroalkanes). 

Examples of the application of the tandem Wittig conjugate-addition sequence to noncarbohydrate y-lactols are shown below. The tricycle 8 was prepared from the lactol 7 in good yield and highly stereoselectively. Upon thermolysis of 8. a retro-Diels-Alder reaction gave rise to furan and to the chiral dihydrofuran 9 in 94% ee36. 

The presence of the triphenylphosphonium substituent makes 351 (Scheme 2.122) an active dienophile. Resulting cycloadducts such as 352 are immediately recognized as precursors for the formation of ylides. Products with an exocyclic double bond such as 353 are easily synthesized via a tandem sequence of Diels-Alder and Wittig reactions. The formation of adduct 353 could have been achieved via the Diels-Alder reaction with the allene CH2 = C = CHR, but this direct route is generally unapplicable owing to the low activity of allenes as dienophiles. 

Horner-Wadsworth-Emmons Reactions of Phosphonate Anions. - As with the Horner modification of the Wittig reaction, the principal focus of papers that mention the Horner-Wadsworth-Emmons reaction relate to synthetic applications. The use of pressure to induce the synthesis of P-amino esters, p-thioesters and P-thionitriles via tandem Horner-Wadsworth-Emmons and Michael reactions has been reported. The reagent (l-tritylimidazol-4-yl)methylphosphonate (99) has been prepared and, when treated with aldehydes and ketones, affords (E)-vinylimidazoles in high yields. ... 

Hartung, R., Paquette, L. Recent synthetic appiications of the tandem Staudinger/Aza-Wittig reaction. Chemtracts 2004,17, 72-82. 

Tandem Michael-intramolecular Wittig reactions of cyclic-ylide (81) with... 

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