Annulenones synthesis

An annulenone synthesis that employs aldol condensations in two key steps is outlined in Scheme 2. Condensation of o-ethynylcinnamaldehyde (18) with acetone provides (19), which is condensed with aldehyde (20) to obtain ketone (21). Intramolecular oxidative coupling of the two alkyne functions affords annulenone (22). 

The Vogel group has also developed rational synthesis of the above annulenones as well as of the other two possible isomers 2,8-14 and 3,9-methano[ 11 ]annulenone 15. 

Ogawa and co-workers37 have reported the synthesis of 6,7-benzo-4,9-epoxy[ 11]-annulenone 60. Manganese dioxide oxidation of the bis(hydroxymethylene)benzo-xepin 57 gave the dialdehyde 58 which on condensation with dimethyl acetonedicarb-oxylate 23 in chloroform in presence of piperidinium acetate gave the diester 59. This on hydrolysis followed by decarboxylation gave the annulenone 60. The NMR spec-... 

An interesting approach to the substituted 6,8-bisdehydro[13]annulenone (238) includes a double Knoevenagel reaction of the mixed acetonedicarboxylic ester (235) with aldehyde (236) in the presence of piperidine to give (237). Oxidative coupling of the acetylene moieties in (237) with Cu(OAc)2 in pyridine affords (238) in 10% yield (Scheme 47).2 a,p-Unsaturated malonodinitriles are suitable intermediates for the synthesis of a variety of carbocyclic systems. Cyclization of the benzylidene malonodinitrile (239) to form a five-membered carbocyclic ring (240) can be achieved upon treatment with acid and subsequent hydrolysis (Scheme 48). A similar cyclization of (241) affords six-mem-bered carbocyclic ring systems. ... 

Diels-Alder reaction The first step in a synthesis of 2-hydroxy-4,10-methano [11] annulenone (7), a lOjr-troponoid, is the reaction of benzocyclopropene (1) with the o-benzoquinone (2). As expected,(7) resemblesa-tropolone... 

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