ALLYLSTANNATION. III. SYNTHESIS OF HOMOALLYLIC ALCOHOLS AND 4-CHLORO-2,6-DIALKYL-3-METHYLTETRAHYDROPYRANS BY REACTIONS BETWEEN (E/Z)-2-BUTENYLDICHLORO-n-BUTYLTIN AND ALDEHYDES

Article abstract of DOI:10.1016/0022-328X(83)80131-4

2-Butenyldichloro-n-butyltin (in various cis/trans isomer ratios) reacts readily with neat RCHO (R = CH3, C2H5, (CH3)2CH, and C6H5) at 25 deg C to give (a) linear alcohols, RCH(OH)CH2CH=CHCH3 in the E and Z forms, (b) branched alcohols, RCH(OH)CH(CH3)CH=CH2 in the threo and erythro forms, and (c) 2,3,4,6-tetrasubstituted tetrahydropyrans (A) as a mixture of cis/trans isomers arising from the CH(CH3)-CHCl bond.The maximum yields of these tetrahydropyrans were obtained by the use of 3-3.5 molar ratios RCHO/tin compound in the absence of solvents, whereas work-up after reactions in CH2Cl2 gave linear alcohols as the main products.The formation of linear alcohols appears to be stereospecific, as the ratio of E/Z isomers obtained is the same as that in the organotin compound.Tetrahydropyrans are formed preferentially as the trans isomers.