THE PREPARATION OF 4-CHLORO-2,6-DIALKYL-, 4-BROMO-2,6-DIALKYL-, (E/Z)-4-CHLORO-2,6-DIALKYL-3-METHYL-AND (E/Z)-4-BROMO-2,6-DIALKYL-3-METHYL-TETRAHYDROPYRANS BY CONDENSATION OF ALDEHYDES WITH DI-HALIDES AND TRI-HALIDES OF ALLYLTIN .9.

The reaction recently discovered leading to tetrahydropyrans (THP): has been more extensively investigated by using various allyltin systems, alternate incremental additions of two aldehydes, and scrambling organotin reagents. Unsymmetric halotetrahydropyrans containing various R groups can be readily prepared in this way. The thermal breakdown of the 12-dichloro adducts, namely (E/Z)1-alkyl-1-butyldichlorostannoxy, 1-alkyl-3-pentyl ethers and the (threo/erythro)-1-alkyl-1-butyldichlorostannoxy, 1-alkyl-2-methyl-3-butenyl ethers, is a stereospecific reaction which affords (E/Z)-halotetrahydropyrans, where the isomerism is at the CHClCH(CH3) bond