A new approach to enantiomerically pure 2,8-dialkyl-1,7-dioxaspiro[5.5]undecanes and 2,7-dialkyl-1,6-dioxaspiro[4.5]decanes is described and utilizes enantiomerically pure homopropargylic alcohols obtained from lithium acetylide opening of enantiomerically pure epoxides, which are, in turn, acquired by hydrolytic kinetic resolution of the corresponding racemic epoxides. Alkyne carboxylation and conversion to the Weinreb amide may be followed by triple-bond manipulation prior to reaction with a second alkynyllithium derived from a homo- or propargylic alcohol. In this way, the two ring components of the spiroacetal are individually constructed, with deprotection and cyclization affording the spiroacetal. The procedure is illustrated by acquisition of (2S,5R,7S) and (2R,5R,7S)-2-n-butyl-7-methyl-1,6-dioxaspiro[4.5]-decanes (1), (2S,6R,8S)-2-methyl-8-n-pentyl-1,7-dioxaspiro[5.5]undecane (2), and (2S,6R,8S)-2-methyl-8-n-propyl-1,7-dioxaspiro[5.5]undecane (3). The widely distributed insect component, (2S,6R,8S)-2,8-dimethyl-1,7-dioxaspiro[5.5]undecane (4), was acquired by linking two identical alkyne precursors via ethyl formate. In addition, [(2)H(4)]-regioisomers, 10,10,11,11-[(2)H(4)] and 4,4,5,5-[(2)H(4)] of 3 and 4,4,5,5-[(2)H(4)]-4, were acquired by triple-bond deuteration, using deuterium gas and Wilkinson's catalyst. This alkyne-based approach is, in principle, applicable to more complex spiroacetal systems not only by use of more elaborate alkynes but also by triple-bond functionalization during the general sequence.
[Show abstract][Hide abstract] ABSTRACT: [Reaction: see text]. The application of fluorous mixture synthesis (FMS) for accessing natural products and their stereoisomers was validated by the total synthesis of all 16 stereoisomers of the pine sawfly sex pheromone. Four fluorous p-methoxybenzyl groups were used as tags, and a "4-mix-4-split" approach was employed in a divergent synthesis. This paper presents the details of the FMS of pine sawfly sex pheromones with an emphasis on identification and solving of problems encountered when working with fluorous mixtures.
The Journal of Organic Chemistry 12/2005; 70(23):9447-62. DOI:10.1021/jo051526a · 4.72 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: (E,E)-2-Alkyl-8-furanyl-1,7-dioxa-spiro[5.5]undecanes (1a–i) have been prepared in good yield and with very high diastereoselectivity from lactones (2a–e) and alkynes (3a,b) using lithium acetylide coupling, hydrogenation, desilylation and acid catalysed cyclisation/equilibration.
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