Synthesis of spiroacetals using organoselenium-mediated cyclisation reactions. X-Ray molecular structure of (2S,8R)-8-methyl-2-phenyl-1,7-dioxaspiro[5.5]undecan-4(R)-ol

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Abstract
Alkenyl hydroxyketones undergo cyclisation via their hemiacetal form, in the presence of N-phenylselenophthalimide (NPSP) and a Lewis acid, to give the corresponding phenylseleno-substituted spiroacetals. Using this methodology the synthesis of trans- and cis-2-methyl-1,6-dioxaspiro-[4.4]nonane (1), trans- and cis-2-ethyl-1,6-dioxaspiro[4,4]nonane (chalcogran)(2), trans- and cis-2-methyl-1,6-dioxaspiro[4,5]decane (3), trans-7-methyl-1,6-dioxaspiro[4.5]decane (4), trans-2-methyl-1,7-dioxaspiro[5.5]undecane (5), and (2S,8R)-8-methyl-2-phenyl-1,7-dioxaspiro[5.5]undecane-4-one (6) has been achieved, after reductive removal of selenium using Raney-nickel in diethyl ether. Compound (2) is the principal aggregation pheromone from Pityogenes chalcographus(L), whilst compounds (3) and (4) constitute the pheromone components of the common wasp, Paravespula vulgaris. The structure of the spiroacetal (6) was determined as a result of X-ray crystallography of a later derivative, obtained by sodium borohydride reduction of (6).