Download e-book for kindle: 178 Topics in Current Chemistry: Small Ring Compounds in by Armin de Meijere, A. Brandi, F.M. Cordero, A. Goti, T. Hirao

By Armin de Meijere, A. Brandi, F.M. Cordero, A. Goti, T. Hirao

ISBN-10: 3540604952

ISBN-13: 9783540604952

This paintings on small ring compounds in natural synthesis covers cycloadditions onto methylene- and alkylidenecyclopropane, and selective modifications of small ring compounds in redox reactions.

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Extra info for 178 Topics in Current Chemistry: Small Ring Compounds in Organic Synthesis V

Example text

Cycloadditions of nitrones to biocyclopropylidenes 3 and 311 Entry BCPs Nitrone 3 1~+ Me"N'O255 1 /--k 2 3 Reaction conditions Benzene, 60 °C, 30 days O280 Me~. ) ! ~---Iq. ~ 18 days Me" Mel "O" ~/ 320a + ~r--l~ ~ / 91 Me- Me O %r"CO2Me 320b 45 A. Goti et al. (Table 23, entry 1) identified as two pairs of 5-spirocyclopropanepyrroloisoxazolidines 288a and 288b and 4-spirocyclopropanepyrrolo-isoxazolidines 289a and 289b. The more regioselective nitrone 257 gives only two diastereoisomers 294a, b in almost 1:1 ratio (Table 23, entry 4).

T. t. t. 2d Products 212 (Yield%) a (76) b (99) c (93) d (94) e (100) f (96) g (16) h (60) i (49) Cycloadditions onto Methylene- and Alkylidenecyclopropane Derivatives containing one, two, or three heteroatoms. The extension of this methodology to methylene- or alkylidenecyclopropane dipolarophiles gives a unique entry to spirocyclopropane-anellated heterocycles. Such compounds are, by themselves, capable of considerable biological activity [52], or, combining the heteroatom functionality and the strained cyclopropane ring, are the candidates for synthetically useful selective transformations [8].

The ease with which nitrones undergo cycloadditions to a tetrasubstituted olefin like 3 must be related to the high energy of the H O M O of the dipolarophile (see Sect. 1). This factor renders comparable the reactivity of BCP (3) and MCP (1), which has a lower lying HOMO, despite the less steric hindrance of 1. The cycloadditions of nitrones to methylenecyclopropanes 285-287 (Table 23), 299 (Table 24, entry 3), and 311 (Table 25, entry 7) substituted on the ring occur with very high diastereofacial selectivity.

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178 Topics in Current Chemistry: Small Ring Compounds in Organic Synthesis V by Armin de Meijere, A. Brandi, F.M. Cordero, A. Goti, T. Hirao


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