¹H‐ and ¹³C‐NMR Investigations of Heptafulvenes

Abstract

'H-and "C-NMR spectra of a series of 8-RI-substituted as well as of 8,8-R', Rz-disubstituted heptafulvenes, varying from inversely polarized (31) to unpolar (3h) and polar heptafulvenes with electron-withdrawing groups (3d, e, 0, have been analyzed and compared with those of methoxytropylium salt 5a. The results concerning 3J (H,H) values and '3C-chemical shifts are shown in Figs. 5 and 6. It turns out that all the NMR parameters are strongly influenced by substituents R', R2, but, contrary to planar pentafulvenes, no linear correlations of the NMR parameter us. Hammett substituent constants u+ are obtained in the series 31 + 3d. ' J coupling constants J(2,3)/J(4,5) and J(3,4) are not much influenced by substituent changes in the series 31 + 3h, but are approaching in the row 3h + 3d. Similarly, signals of the I3C-atoms undergo a moderate shift to higher frequencies in the row 31 + 3h but are strongly influenced by -M groups, whereby the sensitivity is decreasing in the series C(7) > C(2)/ C(5) > C(3)/C(4) > C(l)/C(6). These results are essentially explained by a boat conformation of inversely polarized heptafulvenes of the type 31 and an increasing planarization of the ring on going to polar heptafulvenes of type 3d.

Masked Alkyne Equivalents for the Synthesis of Mechanically Interlocked Polyynes**

“…This elimination is accompanied by a skeletal rearrangement: the [4.3.1]propellane undergoes an electrocyclic reaction to form the bicyclo[4.3.1]decane, as revealed by the fact that the bridgehead carbon signal is shifted from 47 ppm in 11 to 140 ppm in 12 . This is in accord with previous reports [15, 31] and the rearrangement is probably driven by the strain in the cyclopropane subunit with an exocyclic double bond.…”

“…Interestingly, this elimination is accompanied by a skeletal rearrangement: the [4.3.1]propellane undergoes an electrocyclic reaction to form the bicyclo[4.3.1]decane, as revealed by the fact that the bridgehead carbon signal is shifted from 47 ppm in 11 to 140 ppm in 12. This is in accord with previous reports [15,31] and the rearrangement is probably driven by the strain in the cyclopropane subunit with an exocyclic double bond. The TMS-alkynes are deprotected using aqueous LiOH to yield masked triyne 13, which can be desymmetrized by statistically protecting one of the terminal acetylenes as the acetone adduct, to give 14.…”

Masked Alkyne Equivalents for the Synthesis of Mechanically Interlocked Polyynes**

“…When 9 is treated with t-BuLi, one bromine is exchanged for lithium and the carbanion can be captured with ketone 10 [30] to install alkyne units in the periphery of the MAE, to give 11,after quenching with TMS-chloride.Another lithiumbromine exchange with t-BuLi eliminates the OTMS group to give masked triyne 12.T his elimination is accompanied by askeletal rearrangement:the [4.3.1]propellane undergoes an electrocyclic reaction to form the bicyclo[4.3.1]decane,a s revealed by the fact that the bridgehead carbon signal is shifted from 47 ppm in 11 to 140 ppm in 12.T his is in accord with previous reports [15,31] and the rearrangement is probably driven by the strain in the cyclopropane subunit with an exocyclicd ouble bond.…”

Rearrangement Reactions of Tritylcarbenes: Surprising Ring Expansion and Computational Investigation

“…Thermolysis of the pure diazo compound 23 f in hexane mainly afforded the alkene 3 f (88 % yield). Analysis of the crude product by 1 H NMR spectroscopy29 revealed that the known30 heptafulvene 5 f was also detected, but only in 0.44 % yield. Such a low proportion was obviously overseen in previous work 3b.…”

“…To complete the reaction, the temperature was increased to 75 °C for 3 h. After removal of the solvent under reduced pressure, a crude residual was obtained as a brown oil, which was purified by flash chromatography (silica gel, hexane/Et 2 O 2:1). The first fraction included 3 f and 5 f 29, 30 (120 mg, 89 %) in a ratio of 200:1.…”