Communications to the Editor 4381 4 5(c 1.35, CHC13), IR (CC14) 1749 cm-'. Exclusive endo alkylation of ketone 8 was accomplished, as anticipated, in 90% yield with methyl iodide using lithium diisopropylamide in tetrahydrofuran (0 °C). That the alkylated product 9, [«]25d -414°( c 1.40, CHCI3), was indeed the product of exclusive endo alkylation was evident from examination of its NMR spectrum at 250 MHz which revealed the C(3) exo proton as a quartet of doublets located at 2.46 (J3 4 = 3.3, Jh ch3 = 7.0 Hz). Baeyer-Villiger oxidation of 9 using basic hydrogen peroxide in aqueous methanol-tetrahydrofuran gave rise to the sensitive hydroxy acid 10 which upon treatment with boron 9 10 trifluoride etherate in methylene chloride at 0 °C rearranged (85% overall) solely to intermediate 4, [a]25p +153°( c 1.50, CHCI3), with the expected transfer of chirality from C(14) -C(16) (steroid numbering). Reduction (¡'-BU2AIH, toluene, -78 °C) of lactone 4, followed by condensation with isopentylidenetriphenylphosphorane (generated with sodium íe/7-amylate in benzene), provided in 50% overall yield dienol 5 as a mixture of double-bond isomers about the C(22)-C(23) olefinic linkage. The required transfer of chirality from C( 16) -* C( 14) was achieved classically by a two-step process. Allylic alcohol 5 was converted (ethyl vinyl ether, Hg(OAc)2, reflux) into its corresponding vinyl ether (82% yield) which upon heating in decalin at 200 °C (5 h) under nitrogen generated aldehyde 6 in 90% yield.7 (6) Our [a]25o for optically pure i in methanol (c 1.00) was +75.2°; however, this value rapidly drops to +60°. Use of dioxane(c 1.00) gave [a]25D +81.8°consistently.
SYNOPSISWe have synthesized and studied the ring dehydration mechanisms and kinetics of polyamic acid models in solution and in the solid state using 13C-NMR (solid and liquid), HPLC, FTIR, and x-ray diffraction. Results obtained in solution show the role of temperature, catalysts, and the basicity of the amine in ring dehydration mechanisms and kinetics, as well as conformation and intramolecular bonds in the amic acid bond in the solid state.
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