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The ring expansion of 7-halogenobicyclo[4.1.0] heptenones and related compounds provides a useful new method for the preparation of the seven-membered conjugated carbocyclic compounds known as tropones and tropolones. This methodology has been exploited in the synthesis of various biologically active troponoid natural products including nezukone, the thujaplicins, thujaplicinol, MY3-469 and colchicine.

C 10 H 16 O 4 cristallise dans P2 1 /n avec a=8.264, b=6.988, c=18.288A, β=96.27°, Z=4; affinement jusqu'a R=0.043. C 16 H 18 O 5 cristallise dans P2 1 /n avec a=12.792, b=8.937, c=13.089A, β=91.37°, Z=4; affinement jusqu'a R=0.048. C 16 H 18 O 5 cristallise dans Pbca avec a=10.773, b=25.953, c=10.818A, Z=8; affinement jusqu'a R=0.048. L'heterocycle dioxolane adopte une conformation entre la demi-chaise et l'enveloppe pour les deux premiers composes, une conformation enveloppe pour le dernier.

One-pot syntheses of the trichlorinated troponoid compounds (8), (10), (12) and (18) have been achieved by reacting tetrachlorocyclopropene (5) with various trimethylsiloxybuta-1,3-dienes.

The title compounds, (3aα,5α,6α)-4,4,6-trichloro-7-methoxy-3,4,5,6-tetrahydro-2H-3a,5-methanoazulene and (3aα,6α)-(E)-8,8-dichloro-5-chloromethylene-6-methoxy-1,2,3,4,5,6-hexahydrο-3a,6-methanο-3aH-indene, both C12H13C130, were formed by mild thermolyses of two related [4.3.1]propellanes and are of interest in the development of new methods for preparing novel analogues of the anti-cancer drug Taxol.

X-ray analyses have established the structures of (3aα,7aα)-6-chloromethyl-8,8-dichloro-2,3-dihydro-5-methoxy-3a,7a-methano-1H-indene, C 12 H 13 Cl 3 O, and (3aα,8aα)6,9,9-trichloro-2,3 5,8-tetrahydro-1H,4H-3a,8a-methanoazulen-5-one, C 11 H 11 Cl 3 O, which have resulted from different modes of cyclopropane ring cleavage within the framework of two closely related gem-di-chloro[4.3.1]propellanes.

The dehydrohalogenation of 8,8-dichloro- and 8,8-dibromo- bicyclo[5,1,0]octa-2,4-diene (4c,d)gives rise to the (E)- and (Z)-isomers of β-t-butoxystyrene (2c). Plausible pathways for the conversion are discussed and evidence in support of bicyclo[4,2,0]octa- 2,4-dienes as intermediates in the conversion is presented. The results support the intervention of halobicyclo[5,1,0]octa-2,4-dienes in the conversion of tetra- and tri-halo-cis-transoid-cis- tricyclo[5,1,0,03,5]octanes (1a-d) to styrenes(2a-c).

Treatment of 4,4,8,8-tetrabromo-cis-transoid-cis-tracyclo[5,1,0,03,5]octane (If) with potassium t-butoxide leads to mixtures of the (E)- and (Z)-isomers of 4- and 3-bronlo-β-t-butoxystyrene (5e,f) and (9e,f) respectively, whereas the 4,4,endo-8-tribromo analogue (1g) affords the parent styrenes (5c,d). On the other hand the tetra- and tri-bromo-cis-transoid-cis-tricyclo[5,1,0,02,4] octanes (8f-h)give complex and unresolved product mixtures. Evidence is presented which eliminates the involvement of halogenocyclooctatetraenes and p-halogenophenylacetylenes in these reactions.

A simple and efficient synthesis of 3,3-dibromo- and 3,3-dichloro-cis- transoid-cis-tricyclo[5,1,0,02,4]-oct-5-ene (3a,b) (gem-dihalo-anti- bishomobenzenes) has been developed from bicyclo[4,1,0]hept-3-ene (9).