3.4- Dimethyl-1 -phenylphosphole

Reaction of the 3,4-dimethyl-1-phenylphosphole (L) complex [PdLjClj] with 1-vinylimidazole in the presence of silver perchlorate carried out in... 

Another A" -phosphorin synthesis from phospholes involves a 1,5-shift of the phenyl group of 1-phenylphosphole into the 2-position. 3,4-Dimethyl-1-phenylphosphole and 1,2,3-triphenylphosphole react with diphenylacetylene at 170 and 230 °C, respectively, in this manner (equation 66) (81TL4713, 8UA4595). 

H. Bonnard, and Mathey, J. org. Chem., 1982, AT, 2376). The initial conversions of phospholes into phosphorins involve a number of stages, the first being the treatment of the phosphole with benzoyl chloride in ether in the presence of triethylamine, for example, the preparation of 4,5-dimethy1-2--phenylphosphorin (Mathey, loQ. ait. Tetrahedron Letters, 1978, 133 J.M. Alcaraz, A. Breque, and Mathey, ibid. 1982, 1565). 4,5-Dimethyl-2-pyridylphosphorin is prepared in a similar manner. For the conversion of 1-phenylphosphole to 2--phenylphosphorin and 3,4-dimethyl-1-phenylphosphole to 4,5--dimethyl-2-(furoyl or thenoyDphosphorin see Alcaraz,... 

A (2 + 2)-photoadduct is formed on irradiation of 2,3-dimethylmaleic anhydride with 3,4-dimethyl-1-phenylphosphole. " The photocycloaddition of maleic anhydride derivatives (124) to the alkene moiety in (125) affords the adducts (126) by a straightforward (2 + 2)-addition. The (2 + 2)-photoadducts (127) are readily produced by the dimerization of the corresponding maleic anhydrides in ethyl acetate solution.The intramolecular photochemical cyclization of the succinimide derivative (128) is a key step in the new synthetic approach to the tetracyclic fragment of neotuberostemonine. ... 

An important new development is the demonstration that Diels-Alder reactions with phospholes and fumaronitriles are greatly accelerated under pressure, and this has led to the synthesis of a number of new 7-phosphanorbornene derivatives. Thus, 3,4-dimethyl-1-phenylphosphole reacted with fumaronitrile at 30 C under 9 kbar for 24 h to give an adduct in 67% yield (Equation (8)) <89T7083>. The stereochemistry at phosphorus was confirmed by x-ray analysis. 

Another metal-promoted cycloaddition is found when, in the presence of NiBrj, diphenyl-vinylphosphine acts as a dienophile towards 3,4-dimethyl-1-phenylphosphole (Equation (10))... 

More surprising is the replacement of a carbon substituent on P, as has been observed in the reaction of 3,4-dimethyl-1-phenylphosphole with t-butyllithium (Equation (19)). This is an excellent method for the formation of t-butyl phospholes <720MR(4)171, 72T4i71>. 

The reaction was also attempted on 3,4-dimethyl-1-phenylphosphole oxide generated in the reaction medium the expected cycloadduct was obtained in only 6% yield, dimerization of the oxide being the major reaction pathway. 

Additions to only one double bond of a phosphole oxide are also possible. Diazomethane gives a pyrazoline, thermally converted to a cyclopropano derivative, as has been observed with 1,2,5-triphenylphosphole oxide <65JCS2I84. 7ICJC874) and 3,4-dimethyl-1-phenylphosphole oxide <89T7083> (Scheme 32). 

The orientation of addition of diazomethane is the opposite of that proposed in the earlier work <65JCS2184>. The H NMR spectrum of (158) does support this structure, since large VpH values (14-19 Hz) were observed for the CH2 group. It was also found possible to epoxidize one of the double bonds of 3,4-dimethyl-1-phenylphosphole oxide with m-chloroperbenzoic acid <91HAC359>. The product (159) was a stable solid, a mixture of diastereoisomers (Equation (30)). 

Dimethyl-1-phenylphosphole selenide gave adducts with maleic anhydride (49%) and N-phenylmaleimide (72% <85PS(25)20l . With the triazolinediones, the addition products fragmented easily. 

A Lewis salt (192) of 3,4-dimethyl-1-phenylphosphole with BHj is formed by reaction with H3B SMe2. The reaction occurs rapidly at 0°C and is near quantitative <940M925>. The salt can be deprotonated at a methyl group at — 80°C with sec-butyllithium the allylic ion (193) so produced reacts at the 2-position on protonation or methylation, giving the novel phosphine complexes (194) and (196) that are isomeric with phosphole complexes and can generate the free phosphole isomers (195) and (197) on decomplexation (Scheme 44). 

The P-phenyl group of a phosphole can be directly displaced by reaction with alkyl lithium reagents in TMEDA. Both t-butyl <72T47i> and -butyl <720MR(4)171> have been placed on P by this method. With 3,4-dimethyl-1-phenylphosphole, the former reaction occurred in 70% yield, the latter in 31.5% (with some oxide) (Scheme 79). This method is of considerable value for the introduction of the t-butyl group on phosphorus, as this group cannot be used as the P-substituent in a phosphonous dihalide in the McCormack reaction because of steric restrictions. 

Until 1992, no C-metal derivative of a phosphole was known, and some of the conventional routes to carbonyl derivatives from this type of precursor were not practical. However, 2-bromo-3,4-dimethyl-1-phenylphosphole (273) has now been synthesized (see Section 2.15.12.8 <92BSF486 and this allowed the synthesis of the 2-lithio derivative (274) and its use in various processes (Scheme 84). Thus, the 2-COOH (275) and 2-COOEt (271) derivatives were prepared from this organometallic. Compound (275) is the first example of a phosphole carboxylic acid its properties are yet to be evaluated. 

UV irradiation. Indeed, thermal reaction of 1-phenyl-3,4-dimethylphosphole with (C5HioNH)Mo(CO)4 leads to 155 (M = Mo) and not to 154 (M = Mo, R = Ph). Complex 155 (M = Mo) converts into 154 (M = Mo, R = Ph) under UV irradiation. This route was confirmed by a photochemical reaction between 3,4-dimethyl-1-phenylphosphole and Mo(CO)6 when both 146 (M = Mo, R = Ph, R = R = H, R = R" = Me) and 155 (M = Mo) resulted (89IC4536). In excess phosphole, the product was 156. A similar chromium complex is known [82JCS(CC)667]. Complex 146 (M = Mo, R = Ph, R = R = H, R = R" = Me) enters [4 -h 2] Diels-Alder cycloaddition with diphenylvinylphosphine to give 157. However, from the viewpoint of Woodward-Hoffmann rules and on the basis of the study of UV irradiation of 1,2,5-trimethylphosphole, it is highly probable that [2 -h 2] dimers are the initial products of dimerization, and [4 + 2] dimers are the final results of thermally allowed intramolecular rearrangement of [2 + 2] dimers. This hypothesis was confirmed by the data obtained from the reaction of 1-phenylphosphole with molybdenum hexacarbonyl under UV irradiation the head-to-tail structure of the complex 158. 

E = As, Sb or Bi) react similarly with Grignard reagents, providing routes to cyclic arsines, stibines and bismuthines. Leung s group has reported further applications of asymmetric Diels-Alder cyclisation reactions in phosphine synthesis. A platinum complex chiral auxiliary has been used to promote the asymmetric [4-1-2] Diels-Alder addition of diphenyl(vinyl)-phosphine to 3-diphenylphosphinofuran, giving the eradocycloadduct (70) as the predominant stereoisomer. Related cycloadditions between 3,4-dimethyl-1 -phenylphosphole and ester-functionalised allylic phosphines have provided chemoselective routes to optically-pure P-chiral 1,2- and... 

Leung et al. [152-167] proposed the Diels-Alder reaction of phospholes with various dienophiles catalyzed by palladium complexes 235 as a method for the synthesis of chiral phosphines. The chiral compounds containing S)-ortho-(l-dimethylaminoethyl)-naphthalene palladium 235 were complexed with diene, for example with 3,4-dimethyl-1-phenylphosphole, which then entered into the Diels-Alder reaction with dienophiles (W,W-dimethylacrylamide, styrene, and others) to result in diastereoisomers of entio-amidophosphanorbomenon complexes 236 and 237. After separation, purification, and decomplexation, the... 

Organopalladium complexes containing the (S)-form of ort/jo-palladated (l-(dimeth-ylamino)ethyl)-naphthalene have been used successfully as chiral templates to promote asymmetric cycloaddition reactions between coordinated 3,4-dimethyl-1 -phenylphosphole 8.34 and two dienophiles (A, A-dimethy lacrylamide and styrene) via two pathways, endo (compounds 8.35) with X=C1 and exo (com-ponnds 8.36) with X=0C103, which proceed as shown in Scheme 8.3 [23]. 

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