Thionyl chloride mediated rearrangement

A novel synthetic approach was developed by R.E. Taylor et al. for the preparation of the triene portion of the biologically active polyketide apoptolidin. The allylic chloride substrate was prepared from an allylic alcohol via a thionyl chloride mediated rearrangement. Next, the allylic chloride was subjected to the Ganem oxidation by treating it with five equivalents of trimethylamine A/-oxide (TMANO) in DMSO at room temperature to obtain the desired a,p-unsaturated aldehyde. Interestingly, the original Kornblum oxidation conditions were not well suited for this system because of the required high reaction temperature. 

The synthesis of benzomorphans substituted in the 11-position from a 2-tetralone (Scheme 4.2, p. 157) involves either thionyl chloride dehydration of an 11-methylcarbinol (13a)(9) or a pyrolysis of the corresponding acetate perchlorate (136)methylene derivative (14). Carbocation-mediated processes in bridged compounds of this type are likely to give rearrangement byproducts. Kugita and Takeda(124) isolated from the thionyl chloride route an unstable chloride (203), and the indenotetrahydropyridine (204). Other reports(30 96a,125) of unidentified products from these reactions resulted in an investigation 126 127 of both pathways (Scheme 4.20). 

Reactions, which are seemingly 1,3-sigmatropic rearrangements, have been carried out with various substrates. Cyclopropyl vinyl alcohols have been converted to 3-cyclopropylprop-2-enyl derivatives by treatment with acetic acid, ° pyridinium chlorochromate, thionyl chloride,benzenethiol, and diethylaminosulfur trifluoride, e.g. reaction of 3 with thionyl chloride to give Double bond migration has also been mediated by treatment... 

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