Allylstannation. IX. 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- and tri-halides of allyltin

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