Polycyclic cyclobutane derivatives, synthesis

Intramolecular cyclopropanation of diazoketones to furnish [3.1.0] and [4.1.0] bicyclic systems are the most common and effective reactions in this category. Two recent examples are shown in equations 48 and 49. The bicyclic ketone 34 has been used in the synthesis of polycyclic cyclobutane derivatives, whereas ketone 35 is the key intermediate in the total synthesis of ( )-cyclolaurene. When the olefinic double bond is attached to, or is part of, a ring system, the cyclopropanation process also works well. Copper oxide catalysed decomposition of diazoketone 36 produces the strained tricyclic ketone 37 in 86% yield (equation 50). In another case, in which the cyclopropanation of diazoketone 38 gave stereospecifically the cyclopropyl ketone 39, copper sulphate catalysis was used. The cyclopropyl ketone 39 is the key intermediate in the total synthesis of ( )-albene 40 (equation 51) ... 

For Aldol and Related Reactions. The TMSI/(TMS)2NH combination can be used for the synthesis of polycyclic cyclobutane derivatives by tandem intramolecular Michael-aldol reaction. TMSI-induced diastereoselective synthesis of tetrahy-dropyranones by a tandem Knoevenagel-Michael reaction, has also been developed. More recently, the facile synthesis of a,a bis(substituted benzylidene)cycloalkanones has been reported, using TMSI (in situ generated) mediated cross-aldol condensations (eq 53). ... 

A generally useful synthesis of fused polycyclic cyclobutane derivatives, which provides a valuable complement to the use of dichloroketen, involves as a first stage the acyloin condensation of an appropriate succinate , followed by hydrolysis, acetylation to (24), and reduction with zinc dust (Scheme 11). ... 

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