Skeletal rearrangement of 6,8-dioxabicyclo[3.2.1]octan-4-ols promoted by thionyl chloride or Appel conditions

Abstract

A skeletal rearrangement of a series of 6,8-dioxabicyclo[3.2.1]octan-4-ols has been developed using SOCl₂ in the presence of pyridine. An oxygen migration from C5 to C4 was observed when the C4 alcohols were treated with SOCl₂/pyridine, giving a 2-chloro-3,8-dioxabicyclo[3.2.1]octane ring-system via the chlorosulfite intermediate. Analogous allylic alcohols with endocyclic and exocyclic unsaturations underwent chlorination without rearrangement due to formation of allylic cations. The rearrangement was also demonstrated using Appel conditions, which gave similar results via the alkoxytriphenylphosphonium intermediate. Several reactions of the products were investigated to show the utility of the rearrangement.

Keywords: bicyclic ring; cyrene; levoglucosenone; rearrangement; thionyl chloride.

Figure 1

Previous work on migration reactions in 6,8-dioxabicyclooctan-4-ols [18].

Scheme 1

Structures for 10a–c, preparation of 10d–f, and X-ray structure of 10e.

Scheme 2

Rearrangement reactions for 10a–f promoted by SOCl₂.

Scheme 3

Reactions of allylic alcohols 15 and 18 with SOCl₂.

Scheme 4

Appel reactions of dioxabicyclo[3.2.1]octan-4-ols 10a,e,f and 15.

Scheme 5

Some transformations for the skeletal rearrangement products 11a and 12a and X-ray structure for 24.

Figure 2

Mechanism for the rearrangement of 10, and Newman projection and the X-ray structure of 10d projected along the C4–C5 axis.