Part One. Scope and application of novel intramolecular ene reactions utilizing allenylsilanes as the ene component. Part Two. Approaches to the synthesis of the magellanane group of Lycopodium alkaloids

A novel thermal intramolecular ene reaction of allenylsilanes was developed. Imines, aldehydes and olefins were all found to act as enophiles in these cyclizations. The reaction, which most likely proceeds via a concerted six electron ene mechanism, forms two contiguous stereocenters with a cis configuration. The silyl group on the allenylsilane was found to be an important component of the reaction in order to stabilize the ene transition state. This transition state stabilization allows these allenylsilane ene reactions to proceed at lower temperatures than has been observed in analogous alkylallene ene reactions.; An attempt was made to apply this methodology to the synthesis of 4-epi-ethisolide (142) and meroquinene (212). The key step of this proposed route to 4-epi-ethisolide (142) was to be the formation of the B ring of the target by a stereospecific ene reaction of allenylsilane glyoxylate ester 168. Glyoxylate 168 was prepared from allenylsilane alcohol 169. The absolute stereochemistry in this system was to be derived from the known chiral aldehyde 171. We were unable to achieve the desired chelation controlled addition of ethynylmagnesium bromide to a derivative of aldehyde 171. Also, formation of the glyoxylate 168 in the presence of the allene proved troublesome, leading to the elimination product 207. Since these problems could not be overcome, the synthesis was abandoned.; A stereospecific synthesis of the cinchonine degradation product meroquinene (212) using this allenylsilane ene chemistry was planned. The target was to be formed by an ene cyclization of a suitably substituted allenylsilane ester such as 213. Unfortunately, the formation of the required cyclization precursor was problematic. Mitsunobu reaction of allenic alcohol 239 provided only minor amounts of the desired nitrile 240, while a cuprate addition to propargyl acetate 250 yield a mixture of acetate 251 and nitrile 240. In light of the problems encountered and the poor yield observed in the cyclization of the model allenylsilane 106, this approach to meroquinene (212) was abandoned.