Wittig solid state

An enantioselective Wittig reaction was accomplished by the solid-state reaction of a 1 1 complex of 10b and 122 or 10c and 143 with 141, which gives... 

In the effort to make pure blue-emitting materials Shim and coworkers [146] synthesized a series of PPV-based copolymers containing carbazole (polymers 95 and 96) and fluorene (polymers 97 and 98) units via Wittig polycondensation. The use of trimethylsilyl substituents, instead of alkoxy groups, eliminates the electron donor influence of the latter and leads to chain distortion that bathochromically shifts the emission (Amax = 480 nm for 95 and 495 nm for 97). In addition, a very high PLQY was found for these polymers in the solid state (64 and 81%, respectively). Single-layer PLEDs fabricated with 95 and 97 (ITO/polymer/Al) showed EL efficiencies of 13 and 32 times higher than MEH-PPV, respectively (see also Ref. [147] for synthesis and PLED studies of polymers 99 and 100) (Chart 2.20). 

There is still much to explore. For example, quantitative solid-state Wittig and Grignard reactions await exploration (see less than quantitative examples in [67]). First experiments are promising, but the authors did not yet care for running the reactions to completion or they did not assess the solid state even though interesting stereoselectivities emerged (review in [67]). 

Wittig reactions of cyclohexanone derivatives in their inclusion compounds with the chiral host 5 gave optically active reaction products. For example, when a mixture of finely powdered 1 1 inclusion compound of 5b with 4-methyl-(15a) or 4-ethylcyclo-hexanone (15b) and phosphorane (16) was kept at 70 °C, the Wittig reaction in the solid state was completed within 4 h. To the reaction mixture was added diethyl ether-petroleum ether (1 1), and then the precipitated triphenylphos-phine oxide was removed by filtration. The crude product left after evaporation of solvent from the filtrate was distilled in vacuo to give (-)-4-methyl- (17a) of 42% ee (73 % yield) or (-)-4-ethyl-l-(carboethoxymethylene)cyclohexane (17b) of 45 % ee (57 % yield), respectively [9], Similar reaction of the 1 1 inclusion compound of 5c and c /. v - 3,5 - dime th y I c y c I o h e x a n o n e (18) with 16 gave 19 of 57 % ee in 58 % yield [9],... 

Solid state Wittig-Horner reaction of 4-methyl- (43a), 4-ethyl- (43b) and 3,5-di-methylcyclohexanone (44) as their inclusion complex with optically active host compound and (carbethoxymethylene)triphenylphosphorane (45) gave optically active 4-methyl- (46a), 4-ethyl- (46b) and 3,5-dimethyl-l-(carbethoxymelhy-lene)cyclohexane (47), respectively [16]. For example, when a mixture of the finely powdered 1 1 inclusion complex of 43a with 2b (1.5 g) and 45 (2.59 g) was kept at 70 C, the Wittig-Horner reaction was completed within 4 h. To the reaction mixture was added ether-petroleum (1 1) and the precipitated solid (Ph PO... 

Only three enantioselective Wittig-Homer reactions using optically active reagents have been reported [17J. In comparison with these, the solid state reaction is much more simple and successful. 

Wittig l56) and Waack 157) showed ebullioscopically and osmometrically, respectively, that phenyllithium is a dimer in etheral solvents. Thonnes and Weiss, 58) found a TMEDA complexed phenyllithium dimer in the solid state, and calculations performed by Schleyer et al. 159) similarly showed the dimer to be the most stable species. The 13C nmr spectrum of phenyl-6Li in THF shows a quintuplet at —118 °C which also reveals a dimeric aggregate l49,160). Thus experimental investigations of the structure in solution and in the solid state as well as a theoretical study (corresponding to the situation in the gas-phase) lead remarkably to the same result a phenyllithium dimer structure seems to be the most stable one. 

Phosphorus ylides can also be prepared via solvent-free Wittig reaction in a ball-mill (Scheme 8.8). High-energy mechanical mixing played a critical role in this chemical transformation and was responsible for the amorphization of the reactants and mass transfer in a solid state. 

Particular highlights include the first structurally authenticated example of a phosphonium diylide and the use of ionic liquids as a novel medium for performing Wittig reactions. Ylides, particularly their iminophosphorane counterparts, continue to provide a strikingly rich avenue of coordination chemistry research. A useful study by Pandolfo et al. reports the solid state NMR spectra of several ylides and their complexes, showing that this technique can provide valuable structural information in situations where it is difiicult to obtain solution data due to solubility problems or decomposition. 

An enantioselective Wittig reaction was accomplished by the crystal-crystal reaction of a 1 1 complex of 4 b and 13 a or 13 b with 14, which gives the corresponding (-)-olefm 15 a of 42% ee (73%) or 15 b of 73% ee (73%), respectively, in the yield indicated [12], An enantioselective Michael addition reaction was also achieved in an inclusion complex with a chiral host compound. Treatment of a 1 1 complex of 4 c and 16 with 2-mercaptopyridine 17 in the solid state gave (—)-18 of 80% ee in 51% yield [13]. 

Organic reactions in the solid state, e. g. Baeyer-Villiger, Reformatsky, Luche, Glaser, Eglington, Wittig, Brown. Michael, Robinson often more efficient than in solution. 

Wittig reaction. Solid state powder NMR studies of... 

In phosphazene chemistry, preparation and reactions of small molecule, linear phosphazenes continue to attract interest. This year numerous papers have explored the utility of the aza-Wittig reaction in the synthesis of complex molecules with particular reference to nitrogen heterocycles. In cyclophosphazene chemistry, the shift of emphasis to materials which are monomers themselves or models for phosphazene polymers is apparent. The synthesis and characterization of poly(phosphazenes) is an active area with extensive interest in phosphazene based polyelectrolytes being noted. Solid state NMR has been shown to be a valuable tool for the study of both structure and phase changes in poly(phosphazenes). 

This conclusion is in agreement with a remark of Lewis who stated that slower reacting systems tend to show a greater effect under microwave radiation than faster reacting ones [82]. In this way, during solvent-free Wittig olefination with phosphoranes, it was shown that the benefit of MW irradiation increases with less reactive systems. The best stabilized phosphoranes do not react at all in the solid state with aldehydes or ketones under conventional heating but necessitate MW irradiation [83]. 

Unstabilised a-iodoalkyl ylides (1) have been prepared and used in Wittig reactions to give 1-iodoalkenes with (Z)-stereoselectivity. The P-fluoro-substituted ylides (3), containing a chiral alkoxy ligand, are formed as 1 1 mixtures of diastereoisomers from the corresponding alkoxydifluorophosphoranes (2). However, (3) can be epimerised to predominately (>95% in one case) one diastereomer by treatment with lithium fluoride. The first carbodiphosphoranes (4) and (6) containing a P-H bond have been reported. Compound (4) is thermally stable in the solid state but in solution at room temperature both (4) and (6) slowly isomerise to the ylides (5) and (7), respectively. The structures of all these products are supported by n.m.r. data. 

Balema VP, Wiench JW, Pruski M, Pecharsky VK. Mechanically induced solid-state generation of phosphorus ylides and the solvent-free wittig reaction. J Am Chem Soc 2002 124 6244-5. 

Wittig, J., 1973, The Pressure Variable in Solid State Physics What about 4f-Band Superconductors in Queisser, H.J., ed., Festkorperprobleme - Advances in Solid State Physics, Vol. XIII (Vieweg, Braunschweig) p. 375. 

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