Brominative cyclization

Tetrabromocyclohexa-2,5-dienone in methylene chloride promotes the biomimetic cyclization of linalool and dehydrolinalool to (60 R=vinyl or ethynyl) as the major product with minor amounts of (61 X = Br, R = vinyl or ethynyl) in contrast to brominative cyclization with A/ -bromosuccinimide when (61 X = Br,... 

Brominative cyclization. Treatment of either costunolide (1) or deydro-saussurca lactone (2) with NBS in aqueous acetone at 2(T results in the cyclized hromo lactones 3. 4, and 5, in approximately the same ratio from both substrates.3... 

Brominative cyclization.1 Even though brominative cyclization of y,8-unsatu-rated alcohols usually results in tetrahydrofurans (12, 457-458), reaction of the... 

A new furoquinolinone derivative was synthesized in which the key steps were bromination, cyclization and elimination <02JMC1146>. 

A number of rearranged monocyclofarnesyl sesquiterpenoids have been isolated from the sea hare Aplysia dactylomela. These include dactyloxene-A (23), -B (24), and -C (25) and dactylenol (26) together with its acetate.These compounds are related to other marine metabolites isolated from red algae. Aplysistatin (27), a metabolite of the sea hare Aplysia angasi, has been synthesized by a route which involves Hg -mediated brominative cyclization and a novel oxidative debenzylation step (Scheme 6). ... 

Brominative cyclization of polyenesTreatment of nerolidol (2) with 1 results in formation (in low yield) of a- and / -synderol (3 and 4) and the bicyclic ethers 3/1 bromo-8-epicaparrapi oxide (5) and the Cg-epimer. 

Biomimetic cyclization of polyenes as routes to diterpenoids continues to be explored. The brominative cyclization of geranyl-linalool afforded160 the 3-bromo-manoyl oxide and the boron trifluoride-catalysed cyclization of the diepoxide of p-homogeranylanisole gave 13-methoxy-A-homo-4a-oxopodocarpatrienol.161 Some further synthetic studies of anhydroverticillol have been reported.162... 

The skeleton can be synthesized from myrcene (7) (brominative cyclization was mentioned in Vol. 4, p. 534, Ref. 583), either by reaction with benzenesulfenyl chloride (giving 719), or by epoxidation (to 720) before cyclizing with SnCl4 or trifluoroacetic acid. The cyclized products 721 (R = OCOCF3 or Cl, R = OH or SPh) were converted to the boll-weevil pheromone 722 (R... 

The antineoplastic agent (— )-aplysistatin (998), isolated from the sea hare, is synthesized from (7 )-malic acid via butyrolactone 987 by a biomimetic brominative cyclization of the homogeranyl-alkylated lactone 996 (Scheme 147) [215]. The cyclization occurs in poor yield, and affords a 19 81 mixture of isomeric dihydroaplysistatins (997), the desired isomer being the minor component. The mixture is converted to (— )-aplysistatin (998) and ( + )-12-epiaplysistatin (999) by phenylselenation of the lactone enolates followed by oxidative elimination of phenylselenic acid. The mixture (12 88) is separated by HPLC to give the pure compounds. 

The reaction of nerolidol (144) with 2,4,4,6-tetrabromocycIohexa-2,5-dione results in brominative cyclization in a biomimetic fashion, to furnish a- and /3-snyderols (145a) and (145b) and 3-bromo-caparrapi oxide (146) and its... 

SCHEME 43.34. Mercury-mediated configurationally retentive brominative cyclization. 

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