acetaldehyde in tetrahydrofuran under N2; pinene is added dropwise to the borane-complex in THF at 0°C, stirred for 1 h, then for 2 h at r. t., cooled to -35°C, the alkyne is added dropwise, stirred for 1.5 h, then 5 h at r. t., MeCHO is added at 0°C; refluxed for 12 h, evapd. in vac. at r. t., then the diol in THF is added, stirred for 3 h at r. t., distd.;