Thiol‐Free E‐Selective Approach to Dithiacyclophanes via Ring‐Closing Metathesis

Abstract

Application of cyclophanes is well-established in molecular recognition, supramolecular chemistry and material science. Here, we assembled novel [6,6], [8,6] and [6,3,3] dithiacyclophanes by using three facile steps involving potassium thioacetate, Grignard reagent and ring-closing metathesis (RCM). This strategy provides E-isomers of orthometa-, orthopara-, meta-and paradithiacyclophane de-rivatives selectively by RCM. Sulfur-based precursors (dithiadiformyl compound) are prepared from bromomethyl benzaldehydes instead of thiols as starting materials. The structure of dithiacyclophanes are confirmed unambiguously by singlecrystal X-ray diffraction studies and the distinguishing structural features in isomers of cyclophanes are discussed.

Selectivity: A Goal for Synthetic Economy

“…When the same triquinane 104 was treated with allyltriisopropylsilane, instead of allyltrimethylsilane, the pentaquinane 105 was obtained (Scheme 21). 30 Scheme 21 Conjugate addition and cyclopentannulation of triquinane 104 using allylsilanes By changing the brominating reagent, the mono and dibromination of compound 108 was achieved. These monoand dibromo compounds were subsequently employed as useful precursors for fragmentation methodology (Scheme 22).…”

“…Along similar lines, the sulfone derivative 40 was treated under metathesis and oxidation conditions to produce the desired thiacyclophane 41 . 19a The hydroxy groups present in compounds 33 and 40 were oxidized in the presence of PCC into keto groups to generate RCM precursors 42 and 43 . However, when these were subjected to RCM, even in the presence of an additive (Ti( i OPr) 4 ), the ring-closing products 39 and 41 were not obtained (Scheme 11 ).…”

“…However, when these were subjected to RCM, even in the presence of an additive (Ti( i OPr) 4 ), the ring-closing products 39 and 41 were not obtained (Scheme 11 ). 19b…”