40°C. Slow warm-up to room temperature, column chromatographic work-up (silica gel flash chromatography, elution with a 10 : 1 : 1 mixture of dichloromethane, petroleum ether (30-50°C) and diethyl ether), and Kugelrohr distillation (bath temperature 45 "C at 0.1 torr) afforded the a-methylene-p-lactones 9a-c in 27, 48 and 40% yields, respectively, as pale yellow liquids with a pungent odor. Satisfactory elemental composition (9a exact mass by mass spectrometry and 9b, c combustion analyses) and appropriate spectral data (IR; 'H-and I3C-NMR, MS) substantiate the proposed 3-methyleneoxetan-2-one structures for 9. Significant in this context is that the position of the IR absorption of the exo -C=C-bond in 8 and 9 remained essentially constant at V = 1700-1710 cm-I, while the car-bony1 stretching frequency underwent the expected hypsochromic shift from V = 1790-1795 cm-' in 8 to i;= 1820-1825 cm-' in 9.As anticipated, preliminary results of reactions with 9 reveal that the a-methylene-f-lactones are highly reactive. For example, 9a reacts as dienophile nearly quantitatively with cyclopentadiene, yielding a diastereomeric mixture of [4 + 2]-cycloadducts. At elevated temperatures (ca. 60°C), this highly activated heterocyclic ring system readily polymerizes. The chemistry of these potentially useful building blocks should be of general interest. In view of the high genotoxicity of the analogous a-methylene-y-butyrolactones, which are naturally occurring biologically active compounds,(h1 the potential carcinogenic behavior of this novel class of heterocyclics should be checked.
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