✍ Scribed by Dr. Marcus Böckmann; Prof. Dr. Martin Klessinger
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Table 2. Desrlylation of 4 (SiR, = SiMe,). R' Reaction T I C ] 6A:6B Yield I%] conditions 6A 6 8 ( -)-phenylmenthyl TBAF. THF -78 31:69 26 58 (-)-phenylmenthy) TBAF. THF. HMPT [a] -78 34:66 25 49 (-)-phenylmenthyl TBAF, THF -105 28:72 23 60 (+)-phenylmenthyl TBAF, THF -78 71:29 55 22 (-)-phenylmenthyl CsF, DMFjTHF
-70 31:69 13 29 [a] Hexamethylphosphoric triamide diastereomers (S,S,S)-6A and (R,R,R)-6B (R' = (-)-phenylmenthyl) can be separated easily by flash chromatography. The transformation with the (+ )-phenylmenthyl ester 4e yielded the (S,S,S)-phenylmenthyl ester 6 A as the major product. The absolute configurations of ( S , S , S ) d A and (R,R,R)dB (R' = (-)phenylmenthyl) were confirmed by X-ray crystallography.[' ' I Compounds such as 6 A and 6B are interesting synthetic C-D ring intermediates for the biologically active cardiac gly-c~sides.['~] In order to obtain the equally important trans-annulated C-D building blocks necessary for the synthesis of vitamin Dj,[l4l the tertiary OH group must be eliminated. The transformation of ( S , S , S ) d A in pyridine (Py) and thionyl chloride affords exclusively the P,y-unsaturated compound (S,S)-8, which can then be hydrogenated to furnish the desired trans-hy-drindan~ne.[~] R' ' OAO 63% (S,S)-8, R' = (+)-phenylmenthyl
A solution of TBAF in THF (1.1 M, 0.289 mmol, 0.26 mL) was stirred in anhydrous THF (2 mL) for 20 min at room temperature with activated molecular sieves to bind any residual water in the TBAF solution. The resulting anhydrous TBAF solution Was then added dropwise to a solution of diketone 4d (120 mg, 0.241 mmol) in THF ( 3 mL) cooled to -105°C. The solution was stirred for 20 min at -105°C and subsequently hydrolyzed with NH,CI. The mixture was extracted twice with diethyl ether, the combined organic layers were washed with NaCl solution and dried over MgSO,, and the solvent was removed. Purification by flash chromatography with pentanejether ( S j l ) yielded 62 mg of (R,R,R)-6B (R' = (-)-phenylmenthyl; 60%) and 24mg of (S.S,5')-6A (R' = (-)-phenylmenthyl; 23%). (R,R,R)dB (R' = (-)-phenylmenthyl): colorless crystals: m.p 96 "C; [XI? = -13.37 (c = 0.8 in CHCI,); 'H-NMR (600 MHz): 6 = 0.85 (m, 1 H. C-14). 0.86 (d. 'J=6.5Hz,3H,C-27),0.92(m,1H,C-17),0.98(s,3H.C-10),1.02(m.1H,C-7), 1.09 (m. 1 H, C-15),1 .I9 (s, 3 H. C-19 or C-20). 1.24 (m, 1 H. CX), 1.28 (s. 3 H, C-19 or C-201, 1.39 (m, 1 H, C-6), 1.40 (m, 1 H, C-7). 1.46 (m, 1 H. C-16). 1.51 (m. 1 H, 1.62(m. tH,1.64(m,l H,. 1.72(m,fH,C-8),1.84(m, 1H,C-17),1.89(ddd,2J=12.9,3J=9.4,3.5Hz,1H. C-3),2.03(m.2H.C-3/13).2.15(ddd,2J=l9.3,3J=9.4.9.1H~.1H.C-2),2.49 C-12),4.83(s, 1 H30H),7.12(m. 1 H,Ar), 7.24(m.4H,Ar); I3C NMR(100 MHz)-IR.S(q,C-lO), 21.7(q,C-27), 21.8 (t.C-7). 25.1 (q,C-19orC-20),25.2(t,C-6). 26.5 (t. C-lS), 27.8 (4, C-19 or C-20). 29.11 (t. C-8), 31.2 (d, C-16), 31.3 (t. C-3), 34.2 53.6(s,C-9),75.4(d,C-12),76.9(s,C-4),t25.2(3xd,Ar),127.9(2xd,Ar),~~1.3 (s,C-21), 175.4(s,C-ll),218(s, C-I); MS (EI):m/;(%):426(Mt,2).408(2). 307
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