Ethers from dioxin derivatives

From the o-dichlorobenzene complex, reaction with a dialkoxide can produce a cyclic bis-ether. This idea has been applied in the preparation of benzo-crown ethers [33], their bisthia analog [33], and several dioxin derivatives [34]. 

Chiral l,3-dioxin-4-ones photochemically react intermolecular with (cyclic) ethers, acetals, and secondary alcohols to give the addition products in reasonable yields. The radical addition was completely stereoselective at C-6 of the heterocycle <1999EJO1057>. The exocyclic diastereoselectivity, where relevant, was about 2 1 (Equation 30). In analogy, an intramolecular cascade reaction of a 1,3-dioxin -one derived from menthone was used to get a terpenoid or a steroid framework in optically active form <1997JA1129, 1999JA4894>. 

Functionalised 2,3-dihydro-l,4-dioxins can be synthesised in a three step-sequence from P-keto esters. The key step is the insertion of a Rh-carbenoid derived from an a-diazo-p-keto ester into an 0-H bond of a 13-diol <99H(51)1073>. The reaction of 2-(l,4-dioxenyl)alkanols with silyl enol ethers yields 23-disubstituted 1,4-dioxanes. When 13-bis(trimethylsilyloxy)-cyclobut-l-ene is used, the expected cyclobutanone products are accompanied by a spirocyclopropane derivative <99TL863>. 1,4-Dioxane-monochloroborane 57 is a highly reactive hydroborating reagent <990L315>. 

An interesting application of copper-catalyzed aziridination is the preparation of ( )-olefin dipeptide isosteres based on a diastereoselective nitrene transfer onto chiral ( )-crotylsilanes (eq 86)7 CuOTf catalyzes the formation of an aziridine whose rearrangement after spontaneous desilylation affords allylamines. Excellent levels of acyclic stereocontrol can be achieved via a hydroxyl-assisted aziridination. Copper-catalyzed aziridination of enol ethers also leads to aziridines that undergo spontaneous rearrangement. Thus, CuOTf and particularly CUCIO4 mediate the formation of an a-methylserinal derivative from a 5-methyl-4//-1,3-dioxin (eq 87). ... 

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