Propionyl bromide

A particularly interesting result is that the preferred conformation for 2-bromo-2-methyl-propionyl-bromide is the one with the two bromine atoms eclipsed14s) ... 

Starting from Z-170 and the syn product, syn-173, starting from E-crotylpiperi-dine E-170. Alternatively, the use of the corresponding crotylpyrrolidines and the employment of in situ formed propionyl bromide gave somewhat lower yields and diastereoselectivities (Scheme 35). 

An ester of alanine with an arylaliphatic alcohol has shown promise as a non-tricyclic aiitidepressaiit. It may be speeulated that the hindered milieu of the ester linkage protects the compound from hydrolysis by endogenous esterases. The preparation starts by reaction of pheny-lacctate 83 with methyl magnesium iodide to give tertiary carbinol 84. Acylation with 2-bromo-propionyl bromide leads to ester 85 displacement of halogen with ammonia leads to alaproclate ( 6) [211. 

In a pair of papers last year, Scott Nelson of the University of Pittsburgh expanded the range of the ketene aldol . In the first paper (J. Am. Chem. Soc. 2004,126, 14), he employed a chiral Al-based catalyst 3. This catalyst mediated additions such as propionyl bromide 1 to 2 to give 4 in 98 2 syn/anti ratio and 95% . 

Hydroxy -2- methyl-1 4 - benzisoxazine - 6 - arsinic acid, obtained from 3-amino-4-liydroxyj>henylarsinic acid and a-bromo-propionyl bromide (as described under 3-hydroxy-l 4-benzisoxazine-0-arsinic acid), crystallises from water in colourless, pointed needles, unmelted at 300° C. The calcium salt forms tufts of needles, but the magnesium salt is amorphous. 

Kubisa et al. also used hydroxy-functional PEG after reaction with 2-bromo-propionyl bromide as an ATRP macroinitiator [228]. Their goal, however, was to polymerize ferf-butyl acrylate, rather than St, then to hydrolyze the esters to acid functionality and study the cation binding properties of the doubly amphiphilic block copolymers. They utilized a CuBr/PMDETA catalyst system for the polymerization and, although the macroinitiator was completely consumed, MALDI-TOF analysis indicated that bromine was replaced with a hydrogen at... 

Similar to the synthesis of the difunctional polysulfone macroinitiator, a polyester was used in the synthesis of block copolymers by ATRP. The a, co-dihydroxy terminal polymer was synthesized by the transesterification of 1,6-hexanediol with dimethyl adipate [237]. The end groups were then esterified with 2-bromo-propionyl bromide and the ATRP of styrene yielded the ABA triblock copolymers. 

As another example for one-step functionalization on polystyrene, the Friedel-Crafts acylation with haloacetyl and -propionyl bromide should be mentioned [68,69] (Fig. 19). The haloacylation is performed in nitrobenzene — which has the swelling power of toluene (see Table 3) — catalyzed by aluminum chloride at room temperature for 20 hours, yielding a capacity of 2.2 mequiv. of reactive sites/g of 2% cross-linked polystyrene [69]. The loading with bromoacetyl moieties of 0.05 mequiv./g found in another experiment [68] should be regarded as the lower limit of functionalization for practical use in the Merrifield synthesis. 

In one synthetic approach (Veld 1990, 1992), alanine is first converted to the bromo derivative via the reaction of the diazonium salt of the amine with hydrogen bromide. In the next step the acid functionality is activated by converting it to the acid chloride using thionyl chloride. The activated acid is condensed with a protected a-amino acid to yield the dipeptide intermediate which is then cyclized by heating in presence of Celite (ion exchange resin) to yield the final product. However, the overall yield of this reaction is fairly low. A more elegant approach is shown in Scheme 5. In this approach, an a-amino acid wth a protected side chain (e.g., e-Z-lysine) is reacted with 2-bromo-propionyl bromide under Schotten-Bauman condidons (Fischer 1908) to yield the intermediate 5a, which is then cyclized under basic conditions to the depsipeptide 5b. 

Propionyl bromide mixed with 1-nitro-l-propene, the temp, allowed to rise to 70° and when it starts falling heated to 80° on a water bath before isolation of the product 1,2-dibromo-O-propionylpropionoxime. Y 60%.— Acid catalysts like ZnGlg, ZnBrg, or H2SO4 may be used. F. e., also with ZnGh, s. L. M. Kozlov, E. A. Markovich, and B. G. Liorber, 7K. 30, 1937 (1960) G. A. 55, 6366b. 

The outcome of regioselectivity of acylation of benzopyrazole moiety depends greatly on the electrophiles and the reaction conditions. The use of potassium tert-butoxide as the base and acetyl chloride as the electrophile affords acetylation exclusively at the N-1 position, while the use of propionyl bromide affords a mixture of acylation products (eqs 25-27). 

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