Dimethylboron bromide and diphenylboron bromide: cleavage of acetals and ketals

Nucleotides, Part LIX, Synthesis, Characterization, and Biological Activities of New Potential Antiviral Agents: (2′ - 5′)Adenylate Trimer Analogs Containing 3′-Deoxy-3′-(hexadecanoylamino)adenosine at the 2′-Terminus

“…The reagent 7, useful for cleavage of various cyclic ethers, was prepared from BBr 3 and Me 4 Sn at À 558 under inert-gas atmosphere and final distillation by known procedures [28 ± 31]. During the epoxide-cleavage reaction, the bulky (tertbutyl)diphenylsilyl group of 5 was not attacked by Me 2 BBr, in contrast to some (tertbutyl)dimethylsilyl (tbdms) ethers which readily reacted with Me 2 BBr at room temperature [28]. Furthermore, 8 was obtained by treatment of 9-(3-bromo-3-deoxyb-d-xylofuranosyl)adenine (9) [11] [22] with tbdps-Cl in pyridine within 19 h in 89% isolated yield.…”

New Synthetic Methods Emphasizing Deoxyfluoro Sugars and Protective-Group Strategy

“…Developments in protective-group strategy, including the formation and cleavage of acetals, continue to be of interest in synthetic carbohydrate chemistry (95,96). The attractiveness of the reagent system described here stems from its simplicity, convenience, versatility, and the high yields of the cleavage products.…”

Total Synthesis of (−)‐Ulapualide A: The Danger of Overdependence on NMR Spectroscopy in Assignment of Stereochemistry

“…[26] Significantly, whereas the synthetic diastereoisomer 3 displayed small differences in the chemical shifts of the 13 C NMR spectra with the natural product for the C32 atom (d = 81.0 ppm; cf. d = 81.8 ppm for natural), the C34 atom (d = 26.6 ppm; cf.…”

“…[1b] The synthetic ulapualide A showed identical chromatographic behavior, as well as chiroptical and 1 H NMR spectroscopic data with those of naturally derived material, but very small differences were observed in the 13 C NMR spectra associated with the C32-C34 portions of the structures. The stereochemistry of natural ulapualide A (1), determined from an X-ray analysis of its complex with actin, differs from that of the diastereoisomer 3 at the stereocenters C3, C28, C29, C30, and C32.…”

“…[10] A Wadsworth-Emmons reaction between the aldehyde 9 and the known phosphonate ester 10 [1] using Ba(OH) 2 as base [11] gave the E alkene 11, which, in one step, was then converted into the alcohol 12 a following hydrogenation/ hydrogenolysis in the presence of the Pearlman catalyst [12] (Scheme 2). The primary alcohol group in 12 a was protected as its TBDPS ether 12 b and the dimethyl acetal group was then unmasked selectively using Me 2 BBr in CH 2 Cl 2 at À78 8C [13] to give the aldehyde 13 in excellent yield. A straightforward Wittig reaction between the aldehyde 13 and the phosphorus ylide, derived in situ from the oxazolemethyl bromide 14 [14] and Bu 3 P in the presence of DBU, next gave the E alkene 15 a.…”