Ricciocarpin

The difference in reactivity is perfectly revealed in Metz s total synthesis of the molluscicidal furanosesquiterpene lactones ricciocarpin A (50) and B (51) (Scheme 9) [32]. Attempts to convert acrylate 43 to lactone 44 using Grubbs5 catalyst A or Schrock s molybdenum catalyst B resulted in very low yields of the... 

Scheme 9 Comparison of substrate reactivity and catalyst activity in total synthesis of ricciocarpin A (50) and B (51) [32]...

A recent application of enantioselective conjugate radical additions was seen in the synthesis of (+)-ricciocarpins A and B [95]. The key step in the synthesis was an asymmetric addition of a functionalized radical precursor 141 to afford intermediate 142 (Scheme 37). A chiral catalyst screening revealed that Mgt and bisoxazoline ligand 19 was optimal for achieving... 

Scheme 37 Application of enantioselective conjugate radical addition total synthesis of Ricciocarpin A and B...

The oxypalladation method mentioned above was introduced as a crucial step in the synthesis of several natural products. As shown in Scheme 8.51, Metz and coworkers used this strategy in an enantioselective synthesis of ricciocarpin A [122], Other impressive applications including the acetalization-RCM sequence have been employed in the synthesis of the AB ring of ciguatoxin [123] and of the Q-C fragment of laulimalide [124] (Scheme 8.52). 

Furanyltitanium reagents were shown to add readily to aliphatic aldehydes in the absence of any promoter, providing more desirable yields and stereoselectivity than furanyllithium, magnesium, and zinc reagents. They were employed as key steps in the total syntheses of (+)-dysidiolide <1998JOC228> and (+)-ricciocarpins A and B <20040L1749>, as depicted in Scheme 24. 

An asymmetric intramolecular Michael-aldol reaction which leads to nonracemic tricyclic cyclobutanes is performed by using TMSOTf andbis[(/ )-l-phenylethyl]amine as chiral amine, but only moderate enantioselectivities are reached (eq 68). A similar reaction sequence can also be carried out with TMSOTf and HMDS as base, with (—)-8-phenylmenthol as the chiral auxiliary however, the iodotrimethylsilane-HMDS system is more efficient in terms of yield and diastereoselectivity. The combination EtsN/TMSOTf (or some other trialkylsilyl triflates) has been used to accomplish an intramolecular Michael reaction, which was the key step for the synthesis of sesquiterpene (=E)-ricciocarpin A. ... 

Scheme 7.44 Cascade conjugate hydrogen transfer/intramolecular Michael reaction and application to the total synthesis of (+ )-ricciocarpin A.

Ricciocarpin A, a furanosesquiterpene lactone, was first isolated from an axenic culture of the European liverwort Ricciocarpos natans in 1990. It bears a <5-... 

Michrowska A, List B (2009) Concise Synthesis of Ricciocarpin A and Discovery of a More Potent Analogue. Nat Chem 1 225... 

Agapiou K, Krische MJ (2003) Catalytic Crossed Michael Cycloisomerization of Thioenoates Total Synthesis of (-l-/-)-Ricciocarpin A. Org Lett 5 1737... 

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