Development and Initial Findings

The choice of silyl substituent was based on the durability of a triisopropylsilyl (TIPS) group relative to other, less bulky silyl groups. Other silyl groups, such as tert-butyldimethylsilyl and triethylsilyl, were also investigated during optimization of the reaction conditions, but it became obvious that a more robust silyl substituent was needed to prevent premature termination of the reaction by desilylation to afford 2-chlorodienones such as 73 (Fig. 4.7). 

The majority of yc/n-dichIorocycIopropane substrates examined in this study provided the desired a-chlorocyclopentenones as a result of sequential electrocyclic ring opening and Nazarov cyclization. In general, those substrates lacking additional substitution on the cyclopropane moiety provided products 75 selectively as a result of regioselective elimination to deliver the more electron-rich olefin. The mechanism for this transformation is believed to involve disrotatory halocyclopropane ring opening 

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