Cyclohexane derivatives aldol cyclization

The intramolecular Michael addition of acyclic systems is often hampered by competing reactions, i.e., aldol condensations. With the proper choice of Michael donor and acceptor, the intramolecular addition provides a route to tram-substituted cyclopentanones, and cyclopentane and cyclohexane derivatives. Representative examples are the cyclizations of /3-oxo ester substituted enones and a,/J-unsaturated esters. 

Cyclohexane derivatives, 569 aldol cyclization, 575, 586 alkenylsilanes, 575 C-1 carbanions, 580 cycloaddition processes, 582 cycloaddition reactions, 582 2-deoxystrq)tamine, 571 Dieckmann cyclization, 574 Diels-Alder cyclizations, 571, 582,584, 585, 589... 

Fleet s group have examined the utility of carbohydrate-derived 2-azido- and 2-iodo-lactones for synthesis of novel, highly functionalized cyclopentanes and cyclohexanes. The azido lactone 11 undergoes KF-catalysed intramolecular aldol reaction to give 12 (major) and 13 (minor). The minor isomer arises through epimerization at C5 prior to the aldol cyclization. Lactone hydrolysis of the major isomer leads to 15. Similar hydrolysis of the minor isomer yields 16, and thus epimerization via retro-aldol must precede lactone ring opening via the intermediacy of 14. 

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