Compound 1b
(1aR,5R,5aS,7aS,7bR,7cS)-rel-(±)-1a,5,5a,7a,7b,7c-hexahydro-1a,5,7a-trimethyl-5a-(1E)-1-propen-1-yldifuro[2,3,4-cd:4',3',2'-hi]isobenzofuran-3,6-dione
From: Diels–Alderase-free, bis-pericyclic, [4+2] dimerization in the biosynthesis of (±)-paracaseolide A
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InChIKey GKQLJCDBHWIELK-FQVGXSHLSA-N
Compound data: CIF
Synthetic procedure: See article for the definitive version of this procedure and for full experimental details.
5-Hydroxy-5-methyl-3-(prop-1-en-1-yl)furan-2(5H)-one (3b, 35 mg, 0.23 mmol) was placed in a 2 mL vial with a Teflon cap. The headspace was flushed with N2. The reaction vial was capped and heated to 110 °C for 48 h. The crude mixture was directly subjected to MPLC (hexanes:ethyl acetate = 1:1) to give unreacted 5-hydroxy-5-methyl-3-(prop-1-en-1-yl)furan-2(5H)-ones (3b, 8 mg, E:Z = 3:4) followed by the truncated paracaseolide A analog (±)-1b (13.9 mg, 42%) as a white powder. 1H NMR (CDCl3, 500 MHz): δ 7.26 (dd, J = 7.6, 3.3 Hz, 1H, H4), 5.87 (dq, J = 15.7, 6.5 Hz, 1H, =CHCH3), 5.53 (dq, J = 15.7, 1.6 Hz, 1H, HC=CHCH3), 3.38 (dd, J = 9.5, 3.3 Hz, 1H, H7c), 3.30 (d, J = 9.5 Hz, 1H, H7b), 3.11 (dq, J = 7.4, 7.4 Hz, 1H, H5), 1.80 (dd, J = 6.5, 1.7 Hz, 3H, =CHCH3), 1.76 (s, 3H, (C1a)CH3), 1.63, (s, 3H, (C7a)CH3), and 1.05 (d, J = 7.3 Hz, 3H, H(C5)CH3). 13C NMR (125 MHz, CDCl3) δ 175.3, 166.4, 144.7, 130.0, 129.5, 127.5, 115.6, 114.1, 58.7, 50.4, 46.5, 39.3, 26.9, 25.9, 18.4, and 12.1. IR (neat): 2923, 2854, 1771, 1390, 1312, 1050, and 911 cm-1. HRMS (ESI-TOF): Calcd for (C16H18NaO5)+ 313.1046. Found: 313.1062. mp 200-201 °C.
