Bicycloalkanones inside-outside

First of all, the stereochemistry about the cyclobutane in the photoadducts is cis in almost all cases (equations 64-68). There are rare exceptions, but these usually result from systems where the cy-cloalkenone is larger than six members or when the tethering chain can easily accommodate the trans cyclobutane (equations 6 72). " The most noteworthy exception is the recent example reported by Winkler in which dioxolenone (35) produced exclusively the trans cycloadduct (36) which was readily converted to the smallest known inside-outside bicycloalkanone (37). This photoproduct presumably arises from initial cyclization in the chair-like conformation (38) (equation 73). Similarly, (39) has been converted to the carbon skeleton of the naturally occurring inside-outside bicyclic compound ingenol (equation 74). ... 

---