Dithiin ring, 2,3-dihydro- from

Only a few examples of ring syntheses by transformation of another ring have been published, as exemplified by the preparation of the sultines 168 by ring enlargement of five-membeted thiolane 1-oxides 166 (cf Section 8.10.9.2.3) and the 3,6-dihydro-l,2-dithiins 202 by catalytic transformation of vinylthiiranes 201 (cf Section 8.10.9.4.2). Because possibilities to synthesize six-membered rings with oxygen and/or sulfur as heteroatoms in 1,2-positions are rather limited, these reactions have been covered already in Section 8.10.9 together with alternative syntheses from alicyclic compounds. 

Dihydroxynaphthalene and 9,10-diacetoxyphenanthrene react with 1,2-diols and 1,2-dithiols in a one-pot synthesis of annulated 2,3-dihydro-1,4-dioxins and -1,4-dithiins (Scheme 26) <04TL1343>. The reaction of 2,3-dihydroxynaphthalene with 1,2-dihalogenated aromatic compounds leads to linearly annulated dioxins of particular interest are tri- and tetra-dioxins and various hetero-fused dioxins e.g. 62 (34%). Several examples yield cation radical salts on electrocrystallisation <04T8899>. Linear arrays of fused pyran-dioxin-cyclohexane rings as found in natural products derived from the milkweed family have been described e.g. 63 <04EJO4911>. 

Phosphorus pentoxide (s. a. under MeSO H) 2,3-Dihydro-l,4-dithiin from 1,3-dithiolane ring... 

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