Phenylmagnesium bromide, initiation

Finally, obtaining olefin 93 from the reaction of thiirene oxide 18a with two equivalents of phenylmagnesium bromide may be a consequence of the initial nucleophilic Michael-type addition of the latter across the carbon carbon double bond of the cyclic sulfone22 (see equation 31). 

The preparation reported here is based on the method of Christie and Rapoport.4 9-Bromo-9-phenylfluorene has also been prepared by a light-initiated reaction of bromine and 9-phenylfluorene in carbon disulfide,2 by addition of phenylmagnesium bromide to fluorene36 followed by treatment with acetyl bromide,5 and by treatment of 9-phenylfluorene with N-bromosuccinimide.6... 

A. Preparation of an ether solution of phenylmagnesium bromide (Note 1). Ether (100 mL) is added to magnesium (Mg) turnings (74.6 g, 3.07 mol) in a dry, S-L flask equipped with an overhead stirrer, reflux condenser, and addition funnel. Iodine (several crystals) is added and the mixture is stirred for several minutes (the color dissipates). Bromobenzene (9.23 mL, 13.76 g, 87.64 mmol) is added and the mixture is heated with a heat gun to initiate the reaction. A solution of bromobenzene (322.8 mL, 481 g, 3.06 mol) in ether (600 mL) is added dropwise over 2.75 hr, maintaining a gentle reflux. The dark brown mixture is stirred an additional 3 hr at ambient temperature under nitrogen and then cooled in an ice/methanol bath to 0°C. 

By its characteristic carbonyl IR absorption band the product of intramolecular termination, i. e. the cyclic B-ketoester was detected by Goode et al. (58), Glusker et al. (59), and Owens et al. (6o) as one of the products of the oligomerization of MMA with phenylmagnesium bromide or fluorenyllithium in toluene. The same compound was found by Lochman et al. (61) when using metalated methylisobutyrate as the initiator in a THF/pentane mixture at high initiator/monomer ratios. 

In 1981, Hirao and others reported that the chiral borane-amine complex 25a, derived from (S)-prolinol and 1 equivalent of BH3 THF, enantioselec-tively reduced propiophenone to afford (R )-l -phenyl-1 -propanol (26) in 44% ee9 (Scheme 4.3h). The chiral complex 25b was even better than 25a, affording the same secondary alcohol in 60% ee. Two years after the initial disclosure, Hirao et al. uncovered a new catalyst system that improved the previous experimental conditions dramatically10 (Scheme 4.3i). When the chiral aminoalcohol 27, prepared from (S)-valine methyl ester hydrochloride and phenylmagnesium bromide, was used along with 2 equivalents of BH3 THF, the enantioselectivity of the alcohol 26 jumped to 94% ee. In addition, the reaction time was shortened to 2 hours. 

Under certain circumstances the initially produced anion 330 (equation 99) reacts further leaving the three-membered ring intact". For example, phenylmagnesium bromide reacts with 14 to give the ether 333 which cleaves with acid to salt 19. Where the... 

The progress of the reaction with methylmethacrylate depends somewhat on initiator, temperature and solvent. Investigations have been carried out using fluorenyllithium [167, 168, 170], phenylmagnesium bromide [171, 172], butyllithium [173] and 1,1-diphenylhexyllithium [174] in toluene solution with or without the presence of ethers. Product analysis shows that two basic reactions occur with the monomer both with magnesium compounds [171, 175] and with butyllithium [176], viz. 

An alternating copolymer of 2-vinylpyridine and a-stilbazole was obtained in toluene at 50X, using phenylmagnesium bromide as initiator [116]. This crystalline copolymer melted at about 350°C. a-Stilbazole alone does not homopolymerize in the presence of organomagnesium compounds. 

Formation of 1,3,5-triazine derivatives has also been observed in the reaction of 3-halo-5-phenyl-1,2,4-triazines with potassium amide in liquid ammonia (80JOC881) and on treatment of 3-chloro-5,6-diphenyl-l,2,4-tri-azine with phenylmagnesium bromide (83IJC(B)559). Both transformations were assumed to be initiated by the addition of the nucleophile employed at C-5 of the 1,2,4-triazine ring. 

One of the virtues of the Braun reagent is that both enantiomers are available, since the chiral diol is made by reaction of phenylmagnesium bromide with (/ )- or (5)-methylmandelate. An application of the (5)-enantiomer is shown in equation (123). The initial aldol reaction was carried out with the magnesium enolate in THF at -78 C to give the diastereomeric aldols in a ratio of 97 3. Transesterification with methanol gives -hydroxy ester (207) in 94% enantiomeric excess. 

The reaction of acetone with phenylmagnesium bromide is. however, very fast 261. In this reaction there is obv iously no need for an initial breaking of the carbon mtignesium bond. In the reaction the new bonds are formed in concert with the breaking of the old bonds. The concerted reaction, however, requires a close approach of the two molecules. 

---