Cheleotropic extrusion of SO2 from readily prepared 3-vinyl-2,5-di hydrothiophene 1 ,I -dioxide 2 provides a clean and efficient route to [3]dendralene (3-methylenepenta-l,4-diene I), the simplest member of the diene-transmissive polyenes, which contrary to previous reports is a stable, easily handled compound that shows unexpected selectivity in Diels-Alder cycloadditions, thus enhancing its utility as a tandem annelating reagent.

The molecular structure of 3,4-dimethylenehexa-1,5-diene ([4]dendralene), C(8)H(10), has been determined in the gas phase. A single conformer with C(2) symmetry, having two almost planar, anti butadiene groups orientated with a dihedral angle C(2)C(3)C(4)C(5) of 71.7(19) degrees, is detected by electron diffraction employing flexible restraints derived from ab initio computations. Other experimental structural parameters (r(alpha)/pm, angle(alpha)/ degrees ) are: C(1)=C(2) 133.4(1), C(3)=C(7) (not in main chain) 134.0(1), C(2)-C(3) 147.4(2), C(3)-C(4) 149.6(3), C(1)C(2)C(3) 124.4(3), C(2)C(3)C(4) 119.2(5), C(4)C(3)C(7) 117.6(7), and C(7)C(3)C(2)C(1) -174.8(28). Ab initio computations at the MP2/6-311G level predict that the vapor consists of ca. 90% of the conformer found experimentally, the other 10% comprising four other conformers.

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Thermal elimination of isobutene and C 0 2 from N-tert-butoxycarbonylaziridino[2',3': 1,21[60lfullerene 4 provides a clean and efficient route to aziridino[2',3': 1,21[60lfullerene 1, an isolable and stable solid.

Contrary to a previous report that Birch reduction of c 6 0 affords C60H36 as the principal product, laser desorption-laser photoionisation time-of-flight (LZTOF), laser desorption Fourier transform io'n cyclotron resonance (FTICR), and liquid secondary ion mass spectrometry (LSIMS) show collectively that a mixture of polyhydrofullerenes, containing &OH18 through to C60H36 with a skewed distribution centred on C60H32 is formed, the discrepancy in results arising from the thermal lability of this mixture of polyhydrofullerenes when subjected to the elevated temperatures (>250 "C) required for mass spectroscopic studies using direct-insertion heated probes.