Asteriscanolide

Scheme 22 Efficient cyclooctene-forming diene-ene RCM, facilitated by cyclic constraint in Paquette s total synthesis of asteriscanolide (116) [75]...

The [4+ 4]-cycloaddition reaction of tethered bis-dienes has been used by Wender and co-workers in total synthesis as exemplified in syntheses of ( )-salsolene oxide and (-l-)-asteriscanolide (Scheme 28). In the synthesis of ( )-salsolene oxide, a nickel(0)-catalyst cleanly effects the cycloaddition of the two conjugated dienes in compound 93 to afford the bicyclo[5.3.1]undecadiene in a good yield and with moderate selectivity.99 The first synthesis of (-l-)-asteriscanolide was accomplished in only 13 steps. The key [4+ 4]-cycloaddition reaction efficiently set the requisite eight-membered ring of (-l-)-asteriscanolide in good yield and with excellent diastereoselectivity.100 The diastereoselective [4 + 4]-cycloaddition has also been applied to the synthesis of the core ring system found in several sesterterpenes such as the ophiobolins (Scheme 28).101... 

Regioselective singlet oxygen ene reactions have been also used, as key steps, towards the synthesis of (+)-asteriscanolide (167) , a-D-sorbofuranose (2S,3R,5R) (168) and a-D-fmctofuranose (2S,3S,5R) (169) ° (Scheme 62). 

Intermolecular PKR is not widely applied. Krafft and co-workers reported the synthesis of asteriscanolide. In their approach, regioslective intermolecular PKR with propene is used for the construction of the cyclopentane backbone of the target molecule (Equation (42)). ... 

Intramolecular [4+4] cycloaddition proceeds smoothly and is a useful reaction. The skeleton 26 of asteriscanolide (27) was constructed by utilizing Ni-catalysed... 

The sesquiterpene (+)-asteriscanolide 1 was first isolated from Asteriscus aquaticus L and characterized by San Feliciano in 1985.1 It has captured the attention of organic chemists mainly because of its uncommon bicyclo[6.3.0]undecane ring system bridged by a butyrolactone fragment. The only prior enantioselective synthesis of 1 has been described by Wender in 1988 featuring an Ni(0)-promoted [4 + 4]-cycloaddition.2 Booker-Milburn and co-workers described the sequential application of intramolecular [2 + 2]-photocycloaddition, Curtius rearrangement, and oxidative fragmentation to produce the 7-desmethyl derivative in 1997.3... 

The preceding synthesis realized by Paquette provides (-i-)-asteriscanolide in 13 steps starting from protected 2-bromo-4,4-dimethylcyclopentenone (2) in an overall yield of 4 %. The key steps are the convergent merging of the readily available enantiopure cyclopentanone sulfoxide 3 and the methyl 4-hydroxybutynoate 14 This domino Michael-Michael addition with a heteronucleophile has... 

Asteriscanolide (65) is a cyclooctane sesquiterpene lactone that has been synthesised by a number of groups who have employed a variety of different strategies. In 2001, Krafft and co-workers developed a strategy that utilised the intermolecular PK reaction as a key step in its synthesis (63- 64 - Scheme 23).71... 

Scheme 23 Cyclopentenone formation in the total synthesis of ( )-asteriscanolide.

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