Claisen/ring-closing metathesis

A novel quinolone-ring fused oxepine 56 (n = 1), reported by Joseph et al., was accessed by a ring-closing metathesis reaction on the precursor 55, which was made in turn from 53 via 54, and a Claisen rearrangement on the last compound. An aza analogue of 56 (n = 1) was made in a similar direct approach <03SL2089>. 

After the development of the modern metathesis catalysts, [185] the synthesis of civetone was one of the first applications of ring-closing metathesis. [186] A Claisen condensation followed by metathesis can be used to prepare civetone, but even under extreme dilution (10" -10 molar), the maximum yield is only 24 %, because of considerable polymer formation. 

Recently Y. Tanabe published a one-pot synthesis starting from methyl dec-9-enoate. [187,188] Key steps are a Lewis acid-catalysed Claisen condensation and a ring-closing metathesis. It is noteworthy that the metathesis proceeds in presence of a titanium enolate complex. Decarboxylation follows spontaneously and gives the product in 48 % yield. 

A review of olefin metathesis has included the application of Claisen rearrangement and olefin metathesis to prepare intricate targets. " Isomerization issues during the ring-closing metathesis step of a new approach towards pentalenene have been reported (Scheme 74). " ... 

Chelate Enolate Claisen Rearrangement 249 Tab. 5.2.6 Domino glycolate Claisen rearrangement/ring-closing metathesis. 

Very recently, Hong et al. [48] used the chelation-controlled Ireland-Claisen rearrangement of 89 in their synthesis of carbovir analogues 91. Herein, again the ring was closed via ring-closing metathesis. 

The EF-ring of ciguatoxin 3C has been stereoselectively synthesized by iterative use of a cyclic ether formation process based on chirality-transferring Ireland-Claisen rearrangement and ring-closing alkene metathesis (Scheme 21). ... 

---