Alkoxycyclization

Examples of these alkoxycyclizations have been applied by Krause to the synthesis of the alkaloids (-)-isochrysotricine and (-)-isocyclocapitelline (equation 104) and fura-nomycin derivatives. ... 

Scheme 58. Cycloisomerization or alkoxycyclization reactions catalyzed by Au(I) halides.

Electron-rich aromatic and heteroaromatic compounds add to 1,6-enynes in the presence of Au(I) catalysts (equations 62 and 63). This reaction leads stereospecrfically to adducts related to the products in the alkoxycyclization by nucleophilic addition on cyclopropyl gold carbene intermediates. Interestingly, in a few cases, addition of the nucleophile takes place at the carbene carbon to give adducts of the type in equation (63). ... 

More recently, Echavarren and coworkers performed a detailed investigation of the enantioselective alkoxycyclization of functionalized enynes with gold (1) complexes in the presence of a variety of chiral ligands such as BEMAP, chiral 1,2-ferrocenyl phosphines and chiral 1,2-ferrocenyl-P N bidentate ligands. " Interestingly the authors... 

Enantioselective selective alkoxycyclization of enynes by (R)-TolBlNAP(AuCl)2 complex. 

Various other nucleophiles can be employed for the trapping of cyclopropyl gold carbenes formed by cycloisomerization of 1,6-enynes. The intermolecular hydroxycyclization or alkoxycyclization of 1,6-enynes in the presence of water or alcohols is also catalyzed by Pt(II) or Pd(II), but they proceed under milder conditions and more efficiently in the presence of cationic gold(I) catalysts. ... 

Charruault, L., Michelet, V., Taras, R., Gladiali, S. and Genet, J.-P. 2004. Functionalized carbo- and heterocycles via Pt-catalyzed asymmetric alkoxycyclization of 1,6-enynes. Ghent. Gommun. 850-851. 

Scheme 930 Enantioselective alkoxycyclization catalyzed by chiral gold complexes.

Water and alcohols can act as nucleophiles in the gold-catalyzed intra- " and intermolecular " reaction with 1,6-enynes. The asymmetric version of the reaction proceeds with good to excellent enantioselectivity using chiral gold complexes [208-210]. The hydroxy- and alkoxycyclization of 1,7-enynes takes place in a similar way [211]. Furthermore, this methodology has been extended to other... 

The defining motif of the plakortones is a sterically congested 2,6-oxabicyclo[3.3.0]octan-3-one moiety, emblematic furanolactone core. This core is accessed efficiently by a palladium(II) mediated alkoxycyclization-lactonization cascade with an appropriate ene-l,3-diol following a typical procedure. Two research groups " independently published their synthetic studies toward functionalized plakortone cores by this domino process (Scheme 15.17). 

SCHEME 15.17. Pd-catalyzed alkoxycyclization-lactonization cascade in the syntheses of plakortones. 

Allyl silyl alkynes 74 react similarly with alcohols in the presence of gold(I) catalysts to give the alkenylsUanes 75 and/or products 76 of alkoxycyclization... 

Scheme 42 Intermolecular Au(I)-catalyzed hydroxy- and alkoxycyclizations of 1,6-en3uies...

Scheme 47 General mechanism for the gold(I)-catalyzed hydroxy- and alkoxycyclization of 1,6-enynes...

Munoz MP, Adrio J, Carretero JC, Echavarren AM (2005) Ligand effects in gold- and platinum-catalyzed cyclization of enynes chiral gold complexes for enantioselective alkoxycyclization. Organometallics 24 1293-1300... 

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