A Novel Three-Component Reaction of Triphenylphosphine, DMAD, and Electron-Deficient Styrenes: Facile Synthesis of Cyclopentenyl Phosphoranes

Abstract

The zwitterion formed from triphenylphosphine and DMAD adds to electron-deficient styrenes to form stable cyclopentenyl phosphoranes. This is the first example of such a zwitterion in which the phosphine is incorporated into the product Ever since the pioneering work of Horner, 1 the zwitterion derived from triphenylphosphine and DMAD has been the subject of several investigations. 2 Following the early work of Winterfeldt, 3 Nozaki et al. have shown that the zwitterion reacts with activated carbonyl compounds to afford highly functionalized g-butyrolactones. 4 We have demonstrated that the activated carbonyl of benzoquinones can successfully take part in these reactions thus constituting a facile synthesis of spiro-fused heterocyclic compounds. 5 Noteworthy in this context is the work of Trost 6 and Lu 7 who have developed intra-as well as intermolecular two-component transformations of electrondeficient alkynes and allenes catalyzed by triphenylphosphine. In the majority of these reactions phosphine plays a catalytic role. There are also reports of reactions in which the phosphine moiety participates in an intramolecular Wittig-type reaction leading to its ejection as triphenylphosphine oxide. 8 In this paper we detail the three component reaction of triphenylphosphine, DMAD, and arylidene malononitriles yielding stable cyclopentenyl phosphoranes. 9Our studies were initiated with 4-methyl dicyanostyrene (1a) which on treatment with DMAD and triphenylphosphine in anhydrous DME as solvent at room temperature yielded a highly polar phosphorane 4a as the product within two hours in 63% yield. Similar reactivity was observed with other dicyanostyrenes and the results are summarized in Table 1.The cyclopentenyl phosphorane structure of 4a was assigned on the basis of spectroscopic analysis. The IR spectrum of 4a revealed the ester carbonyl absorption at 1743 cm -1 , while that of the cyano group was at 2242 cm -1 , and the carbonyl adjacent to cyano was observed at 1660 cm -1 . The methoxy protons of the ester group in 4a were discernible at 2.86 ppm in the 1 H NMR spectrum. The 13 C NMR signals for the carbonyls were seen at 180.8 and 165.9 ppm, the latter corresponding to that of the ester. Conclusive evidence for the structure was obtained by single crystal X-ray analysis (Figure 1). Figure 1Single-crystal X-ray structure of 4a

Synthesis and Reactions of Stabilized Phosphorus Ylides

“…The phosphorane (159) can be oxidized by a methanolic solution of cerium (IV) ammonium nitrate (CAN) in an oxygen atmosphere. A mechanistic rationale for the formation of phosphorane (159) may be outlined as follows: Initially formed zwitterionic intermediate (3) from the reaction of (1) and (2) adds to the activated styrene (158) in a Michael fashion to yield a betaine (161); latter on cyclization and subsequent deprotonation can deliver the phosphorane (159) (Scheme 43) [170].…”

“…Stable crystalline phosphorus ylides (171) are obtained in excellent yields from the 1:1:2 addition reaction between trialkyl phosphites (170) and (2) in the presence of arylsulfonyl isocyanates (167). On the basis of the well established chemistry of trivalent phosphorus nucleophiles, it is reasonable to propose that phosphorane (171) results from initial addition of trialkyl phosphite (170) to the acetylenic ester (2) and subsequent attack of the resulting zwitterion (172) on the arylsulfonyl isocyanate (167) to yield betaine (173).…”

“…On the basis of the well established chemistry of trivalent phosphorus nucleophiles, it is reasonable to propose that phosphorane (171) results from initial addition of trialkyl phosphite (170) to the acetylenic ester (2) and subsequent attack of the resulting zwitterion (172) on the arylsulfonyl isocyanate (167) to yield betaine (173). This is followed by attack of the second arylsulfonyl isocyanate (167) to yield betaine (174), which apparently cyclizes under the reaction condition employed to produce the hydantoin (171) (Scheme 46) [173].…”

“…On the basis of the well established chemistry of trivalent phosphorus nucleophiles it is reasonable to propose that 1,2-oxaphosphole (176) results from initial addition of (1) to the acetylenic ester (60) and subsequent attack of the resulting anion (177) on the carbonyl carbon (ketone) of ethyl 3-bromopyruvate (175) to yield betaine (178) which apparently cyclizes, under the reaction conditions employed, to produce the 1,2-oxaphosphole compounds (176) (Scheme 47) [174]. The reaction of (2) and 2-naphthol (110) in the presence of trimethyl or triphenyl phosphite (170) leads to 4H-1-oxa-2 5 -phosphaphenanthrene-3,4-dicarboxylate derivatives (182) in high yields (Scheme 48) [175].…”

Triphenylphosphine promoted addition of acetylenic esters to benzofuran-2,3-dione: One-pot synthesis of novel γ-spirolactones

“…[16][17][18] We have also demonstrated that the activated carbonyl of phenyl glyoxalate and isatin derivatives can take part in such reactions successfully, thus constituting a ready synthesis of heterocyclic compounds. [19][20] We now wish to report a simple one-pot three-component reaction between dialkyl acetylenedicarboxylates, Ph3P, and benzofuran-2,3-dione derivatives leading to methyl 4'-methoxy-spiro[benzofuran-3,2'-furan]-2,5'-dione-3'-carboxylate derivatives as γ-spirolactone systems (Scheme 2 and Table 1 …”