Abstract
Bicyclo[4.2.0]oct-2-en-7-ones (1)–(4) provide the corresponding 2-bromo derivatives (5)–(15) through a range of highly stereoselective reactions. From chosen compounds in the latter series, the tricyclo[3.3.0.0]octanones (16)–(22) were prepared. The tricycles (16) and (18) provided the bicyclo[3.3.0]octenones (23) and (24) respectively on treatment with acid or base. The reaction of the ketone (19) with nucleophiles (such as azide, fluoride, or iodide ion) gave the appropriate product (27), (29), or (30) derived by a regiospecific homo-conjugate addition process. Cyanide ion converted the diphenyltricycloalkanone (22) into the cyano ketone (32) in like manner but this strained ketone (22) reacted in a different way with methoxide ion to give the methyl esters (33) and (34). Treatment of the tricycloalkanones (19) and (22) with bromine gave the 1,4-dibromobicyclo[3.3.0]octan-2-ones (38) and (39). The structure of the compound (20) was confirmed by X-ray crystallography. Dehydrobromination of the 2-bromobicycloheptan-6-ones (43), (45)–(47), (49), and (50) gave the series of tricyclo[3.2.0.0]heptanones (51)-(56). While the dimethyltricycloheptanone (55) reacted with methoxide ion and toluene-α-thiolate ion to give the ketones (57) and (58) as the major products, the analogous diphenyl compounds (52)–(54), and (56) reacted with various nucleophiles to regenerate the bicyclo[3.2.0]heptan-6-one ring system. The reaction of compound (54) with methoxide ion was exceptional; the esters (66), (68), and (69) were formed in the ratio 13 : 5 : 4. Bromine added to the tricyclo[3.2.0.0.1,4]heptanone (53) to give the dibromo ketones (71) and (74) in the ratio 2 : 3. The tricycloalkanone (54) behaved in a similar manner. The lactone (79) was prepared and a crystal structure was obtained by X-ray analysis allowing the crystal structures of compounds (20), (52), and (79) to be compared. The bicycloheptenone (2) was partially resolved using Clostridium spp.
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