Acetylenic oxy-Cope rearrangement

Acetylenic oxy-Cope rearrangement (12, 51). The oxy-Cope rearrangement of 5-hexen-l-yn-3-ols is accelerated in refluxing N-methyl-2-pyrrolidone (9, 316), but the required temperature (165°) can result in rearranged products. The rearrangement can proceed at 20-60° in the presence of silver trifiate (1 equiv.), which is known to complex with triple bonds.2. ... 

The selective synthesis of pseudoionone is achieved by the acetylenic oxy-Cope rearrangement of 4-isopropenyl-3,7-dimethyl-6-octen-l-yn-3-ol (37) in A-methylpyrrolidone (NMP) as solvent containing a trace of hydrobromic acid, or iodine772,1127. 

Other Degraded Carotenoids. Several syntheses of ionones and related compounds have been described. Some of these may prove useful for end-group construction in carotenoid synthesis. Thus 4-keto-j8-ionone (126) and 3,4-dehydro-jS-ionone (127) have been prepared by condensation of the sulphone (128) with propylene oxide, followed by elimination of phenylsulphinic acid and either oxidation or dehydration. A novel method utilizes a thermal acetylenic oxy-Cope rearrangement process to prepare the ionone compounds (129—131 R = Me) and analogues (R = Et or Pr ) from cyclohex-2-enylprop-2rynols (132). 

The power of pericyclic reactions for forming new carbon-carbon bonds is nicely illustrated by the use of the Claisen orthoester rearrangement to prepare y-ketoesters with a quaternary centre next to the ketone (Scheme 9)The use of silver salts to catalyse the acetylenic oxy- Cope rearrangement for the preparation of a,0-6,e-unsaturated ketones has also been reported [equation (10)].57... 

A selective one-pot synthesis of pseudoionone (76) from the unsaturated alcohol (77) has been achieved by an acetylenic oxy-Cope rearrangement followed by a double-bond migration (Scheme 123). The process, designed for large-scale industrial use, was also successfully applied to related systems. 

Miscellaneous Reactions. AgOTf induces a highly diastere-oselective cyclization of amino ketenes wherein asymmetry is induced by an adjacent stereogenic center and is dependent upon silver concentration (eq 6). Acetylenic oxy-Cope rearrangements are also facilitated by AgOTf (eq 7), and a mild, high-yield esterification utilizes AgOTf in the presence of titanium(IV) chloride (eq 8).4... 

Oxy-Cope rearrangement of acetylene derivatives 42 gives cyclooctadienones1012. The rearrangement of enynol 45 is applied in the synthesis of poitediol. The synthesis of ( )-phorcan-tholide I is achieved from substrate 471128. 

Bis-acetylenic alcohol 1 undergoes a facile oxy-Cope rearrangement to afford mixtures of ( )-and (Z)-enynones. The latter compounds react further to give spiroannulated methylenecy-clopentenone 4 upon enolization and clectrocyclic ring closure1134. 

Their attempted total synthesis of geigerin started from the acetylenic ketone 197, which was generated in 76% yield from the oxy-Cope rearrangement of... 

The 9-membered cyclic ethers 116 have been prepared via oxy-Cope rearrangement of 115, ultimately derived from D-glucose. The 10-membered bis-ether 118 was prepared via Bergman cyclization of the bis-acetylene 117 (R=2,3,4,6-tetra-0-benzyl-p-D-glucosyl). Solution conformational analysis was reported from NMR experiments. Dialkyne 117 was prepared by Pd-catalysed coupling of the P-D-glucosyl-l-alkyne and 1,2-diiodobenzene, and a mechanism was proposed for... 

A useful application of the oxy-Cope rearrangement has been used to produce conjugated enynes [e.g. (114) - (115)]. The enyne (115) is an intermediate in a synthesis of the sex pheromone of the Pine Sawfly Neodiprion lecontei. Potassium t-butoxide in liquid ammonia has been found to be the preferred base to produce high yields of the conjugated 1-alkylthio- or l-arylthiobut-3-en-l-ynes (117). Elimination of thiols from the acetylenic disulphides (116) under these conditions completely suppresses the competing formation of cumulene or diene-sulphides. 

Precursors for an allene oxy-Cope variant are readily prepared from acetylenic derivatives. Rearrangement of allenic alcohol 11 yields a 1 1 EjZ mixture of 121108. 

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