Cyclobutanes from epoxide openings

Liu has reported recently a new Co2(CO)8-mediated tandem [5+ 1]/ [2 + 2+ 1]-cycloaddition reaction that gives tricyclic 5-lactones from cis-epoxy enynes 186. This process possibly involves an initial opening of the epoxide in the cobalt hexacarbonyl complex 187 to from the complexed al-lene 189 via 188. Further coordination of the tethered olefin leads to 190 and further oxidative cyclization gives cobaltacycle 191 which inserts CO leading to the final compound 192. When performing the reaction under N2,191 suffers a reductive elimination to give cyclobutane 193 (Scheme 55) [172],... 

The regioselective synthesis of the unnatural cuparenone isomer (C, Scheme 98) has also been performed 135) (Scheme 98b) from the same oxaspirohexane by a two-steps sequence which involves the selective (100%) — opening of the epoxide ring leading to the corresponding 1-(1-hydroxy)-l-(chloromethyl)cyclobutane (BeCl2/ THF, 20 °C, 20 hr) and its further transformation to the cyclopentanone C is achieved 13S) with silver tetrafluoroborate on alumina. 

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