Ein neuer Zugang zu 17α‐Brom‐ und 17α‐Iodethinyl‐Steroiden

Abstract

Der Austausch des H‐Atoms in CCH durch Br oder I gelingt mit N‐Brom‐bzw. N‐Iodsuccinimid unter Silbersalz‐Katalyse. Mit dieser Methode ließen sich unter anderem zahlreiche 17α‐Brom‐ 2 und 17α‐Iodethinyl‐Steroide 3 herstellen. Anders als bei älteren Methoden müssen Hydroxy‐ (und Carbonyl‐)gruppen in 1 nicht geschützt werden.

Tris(biphenyl‐4‐yl)silyl‐Endcapped Polyynes

“…[16] The synthesis of 4 could also be carried out using 2 under the same conditions. [17] The subsequent synthesis of differentially protected 5 was accomplished under Pd-catalyzed cross-coupling conditions between 2 (or 4) and 6 (or 7) [18] in moderate yield (Table 1).…”

Total Synthesis of Naturally Configured Pyrrhoxanthin, a Carotenoid Butenolide from Plankton

“…Under AgNO 3 catalysis [27] the terminally unfunctionalized alkyne 22 [26] and NBS provided the desired bromoalkyne 10 in 41 % overall yield for the seven steps from 11. Our preparation of the trans-alkenylstannane 12 (Scheme 3) from (À)-actinol (11) followed established procedures.…”

“…[38] A Wohl-Ziegler bromination of crotonic acid (27) and the addition of bromine to the C=C bond yielded 1,2,3-tribromobutyric acid. This compound lactonized in boiling water, whereupon a b elimination furnished the bromobutenolide 31.…”

Total synthesis of polyyne natural products

“…The low yield of the desired product 39 was probably due to an achimerrically-assisted deglycosylation, as reported for 4-pentenyl glucosides [53]. Bromo enyne 40 was prepared from commercially available (E)-2-penten-4- yn-1-ol via (1) hydroxyl protection as the t-butyldimethylsilyl ether, and (2) bromination with NBS in the presence of AgNO 3 [54]. The coupling of bromoalkyne 40 and glucoside 39 was carried out under Cadiote Chodkiewicz conditions which, proceeded with concurrent removal of acetate groups by EtNH 2 , leading to the polar glucoside 41 in 31% yield.…”