Bromo acetates from

Suzuki, T. and Kurosawa, E. (1979) New bromo acetal from the marine alga, Laurencia nipponica Yamada. 1. Chemistry Letters, 301—304. 

The addition proceeds most smoothly with highly functionalized (more polar) steroids as seen in examples by Bernstein and others. The polar reaction conditions pose solubility problems for lipophilic androstane, cholestane and pregnane derivatives. Improved yields can be obtained in some cases by using dimethyl sulfoxide or t-butanol " as solvents and by using sodium A-bromobenzenesulfonamide or l,3-dibromo-5,5-dimethyl hydantoin (available from Arapahoe Chemicals) as a source of positive bromine. The addition of bromo acetate and bromo formate to steroid olefins has been studied to a limited extent. ... 

Fluoroheptyl acetate from l-bromo-2-fluoroheptane and sodium acetate, 46, 37... 

A variety of reaction conditions have failed to produce the 3-bromo derivative from (130), perhaps because ring strain promotes /pso-substitution and macroring opening, whereas (135 n = ll) is brominated (25-30%) with NBS in acetic acid to give (136) (76ACS(B)34l). Ethyllithium reacts with (136) to open the thiophene ring and give (137). 

The results obtained in the methyl D-glucopyranoside series were thoroughly extended to other benzylidene acetals. From methyl 4,6-O-benzylidene-a-D-galactopyranoside (22), the expected 6-bromo derivative 80 was obtained in high yield (90%),116 and methyl 2,3-di-O-... 

Fig. 13. The pH dependence of the esterase activity of native and carboxymethyl-ated human carbonic anhydrase B. The term CM-enzymes refers to Zn(II)-enzyme ( . A) and Co(II)-enzyme (O, A) which had been carboxymethylated with bromo-acetate. Relative activity was estimated in each experiment by taking 100% as the value corresponding to maximal activity of the same enzyme at high pH. This value was 17 min-1 for the unreacted enzyme and 3.5 and 2.1 min-1 for the Zn(II)-and Co(II)-carboxymethylated enzymes, respectively. From Whitney et al. (65)...

Long-chain alkanes. Triphcnylphosphonium salts such as 3, prepared as shown from bromo acetals 2, when treated with dimsylsodium form the long-chain bromo acetal 4. The terminal bromine atom can be displaced by lithium trielhylborohydridc. 

In parallel fashion, compound 267, made from 2,3 5,6-di-<9-isopropyl-idene-D-mannono-1,4-lactone by Reformatsky addition using ethyl bromo-acetate and zinc-silver graphite, undergoes ready elimination when converted to the methanesulfonic ester to give a separable mixture of the E- and Z-alkenes (268).251 Quite a different approach involves treatment of the 1-C-nitromannofuranosyl chloride, derived from the oxime of 2,3 5,6-di-O-isopropylidene-D-mannose, with the anion of diethyl malonate to give the disubstituted alkene 269.252... 

In a parallel study, it was found that chelating chiral diamines 208 or 209 are well suited as ligands to promote Kumada-type couplings of primary and secondary alkyl halides 202 with aryl Grignard reagents 203 (entry 4) [281]. This reaction was applicable to alkyl bromides and alkyl iodides, while alkyl chlorides gave only low yields. Acetal and ester functions are tolerated. A notable feature is the stereoretentive arylation of fra s-a-bromo acetals with excellent diastereo-selectivity. The involvement of radicals is supported by the stereoconvergent formation of cxo-phenvI norbornane from both endo- or exo-bromonorbomane (cf. Part 1, Fig. 9) and radical 5-exo cyclizations (see below). 

The elimination of a molecule of halogen acid from halo acetals of acetaldehyde with powdered potassium hydroxide gives ketene acetals. However, the ti-bromo acetals of the homologs of acetaldehyde on similar treatment with potassium hydroxide or potassium 1-butoxide are converted into ctyjS-olefinic acetals. ... 

Table 6. j8-Elimination from bromo acetal under solvent-free conditions... 

Table 8. Comparison of different modes of activation for j8-elimination from bromo acetal...

In 1975, the Tumor Research Group of the Chinese Academy of Medical Science (47) reported a short synthesis of harringtonine (2) as shown in Scheme 19. Treatment of the olefinic pyruvate 148, obtained from the reaction of cephalotaxine and the corresponding acid, with mercuric tri-fluoroactate, followed by reduction with sodium borohydride yielded the known hemiketal 140. Reformatsky reaction of 140 with methyl bromo-acetate yielded harringtonine (2). 

Trimethylphosphonoacetate, (CHaO PCHjCQjCHa [1, 1235, before Trimethyl-silanej. Mol. wt. 182.11. Preparation from trimethyl phosphite and methyl bromo-acetate (compare triethylphosphonoacetate). 

Fluoroheptyl acetate from l-bromo-2-fluoroheptane and sodium acetate, 46,37 Formaldoxime, 46,13 reaction with 2-bromo-4-methylbeL zenediazonium chloride, 46,14 Formamidine, from hydrogen cyanide,... 

The Bi2-catalyzed electrolysis of acetoxy bromo acetal 19a in DMF at -1.0 V alforded the diastereomeric acetal 20 as a product of a cyclization-elimination sequence. Starting from a chiral cyclopentene bromoacetal (19b) and l-octyn-3-one, a prostaglandin p2a precursor (21) containing all the structural features from C(, to C20 with SR, 11/ , and 12/ chirality, is obtained by the one-step formation of two carbon-carbon bonds in the B -catalyzed radical cyclization addition sequence (Scheme 7) [10]. 

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