Oxaspiro hexanes

Lithium iodide in refluxing CH2C12 has also been used to convert the oxaspiro-hexanes (169) to polyalkylated cyclopentanones (170) (Table 6)59). 

Oxo-4-oxaspiro[2.3]hexanes are rearranged in the presence of a copper catalyst to give 2(5H)-furanones and 2(3/f)-furanones [94]. 

Ozonolysis of 1 gave rise to a mixture of the epoxide 202, spiro[2.3]hexan-4-one (203), and 4-oxaspiro[2.4]heptan-7-one (204). While 202 and 203 apparently... 

The easy cleavage of the oxetane ring with acyl chlorides is well known and was reviewed previously (64HC(l9-2)983). More recently it has been observed that 2-oxaspiro[3.2]hexane was cleaved by acyl bromides to give 1-bromomethylcyclopropylcarbinol esters in high yield (68IZV670). 

Analogous to the procedure for 6-cyclopropyli-dcnc-5-oxaspiro[2.3]hexan-4-one (ref. 57e), but THF has to be employed as solvent instead of acetonitrile. Hoffmann, H. M. R. personal communication to A. de Meijere. 

Expansion of cyciobutanones to cyclopentanones. l-Oxaspiro[2.3]hexanes are isomerized to cyclopentanones in quantitative yield in the presence of Lil. The reaction is a particularly attractive route to 3,3,4,4-tetrasubstituted cyclopentanes... 

Irradiation of the oxygen analog of [53], 1-oxaspiro [2.3]hexan-5-one [58], in methanol afforded similar results (30). In this case however, ring expansion was even more pronounced. As observed for ketone [53],... 

The reaction involving the alkylation of p-hydroxyalkyl selenides to give p-hydroxyalkylselenonium salts which are then cyclized with a base is by far the most general. It allows Ae synthesis of a large variety of epoxides such as tenninal, a,a- and a,p-disubstituted, tri-33-> and tetra-substituted, 3,i88 as oxaspiro[2.0.n]-hexanes, -heptanes and -octanes (Scheme 161, g Scheme 162, d Scheme 164, d Scheme 165, b) - and vinyl oxiranes (Schemes 166 and 181)33 -239 from both p-hydroxy-alkyl methyl33- 3 3 22>.222j36,263 phenyl selenides. ... 

The wide applicability of the cyclopropanation reaction allows the preparation of intermediates for elaborated compounds. The preparation of trans- and cw-l-phosphoryl-5-oxo-4-oxaspiro[2.3]hexanes 1, which are important intermediates for the synthesis of heterocycles or functionalized cyclopenten-l-ones, illustrates well the potential of this reaction. 

In contrast to methylenecyclopropane, bicyclopropylidene reacted with singlet oxygen generated photochemically. The reaction products were 7-oxadispiro[2.0.2.1]heptane and spiro[2.3]hexan-4-one (ratio 10 6). Both compounds were also obtained by reacting ozone with bicyclopropylidene, together with a third product, which was identified as 7-oxaspiro-[2.4]heptan-4-one (relative amount 67%). °... 

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