Bicyclo undecene synthesis

The influence of solvents [64] and comparisons with catalysts of the diarylpro-linol series [65] were reported. For theoretical calculations on stereocontrol see Reference [66]. In addition, imidazolidin-4-one catalyzed cycloadditions have been used in several total syntheses of natural products. Intramolecular Diels-Alder reactions (IMDA) were reported as key steps in the synthesis of bicyclo-undecenes [67], amaminols [68], solanapyrones [69], telomerase inhibitor UCS1025A [70], englerin A [71], (-)-nor-platencin [72], and muironolide A [73]. In addition, asymmetric [3-1-2]-cycloadditions of azomethines were accomphshed in the presence of chiral imidazoUdinones [74]. Intermolecular cycloadditions of dihydropyridine 53 and acrolein catalyzed by imidazolidin-4-ones were reported. The chiral azabicyclo-octenol 54 was isolated as the important key intermediate in the total synthesis of lycopodium alkaloids [75] (e.g., ludduline) and oseltamivir (Scheme 4.19) [76]. 

Majetich reports a general intramolecular Lewis acid allylation protocol for the synthesis of bicy-clo[5.4.0]undecen-3-ones (168) and bicyclo[4.4.0]decen-3-ones (170), which are 1,6-addition products (Scheme 27). The same precursors, (167) and (169), when submitted to the fluoride ion cyclization protocol, also afford 1,2- and 1,4-addition products.73 Typically, ethylaluminum dichloride, a proton sponge Lewis acid, is used in order to minimize adventitious protonic desilylation. Other 0,y-unsatu-rated silanes also undergo similar intramolecular Lewis acid catalyzed additions for example, the si-lylpropargylic enones (171) undergo intramolecular cyclization to the allenylspiro system (172).74... 

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