1.3- dioxolane, basicity structure

Synthesis of model compounds and structural units are being investigated. A double Simmons-Smith reaction on the l,3-dioxolane-4,5-diylbis(alkene) 107 afforded the product 108 with excellent stereoselectivity. The required asymmetry in the double cyclopropanation was the result of coordination of the zinc carbenoid reagent by the Lewis basic dioxolane ring oxygen prior to each cyclopropanation event. The cyclopropanated product was converted to ( )-l,2-bis[(l 5,25)-2-methylcyclopropyl]ethene, a relevant model for the complete structural assignment of FR-900848. 

Compounds with a catechol-type instead of the dioxolane ring A were poorly active [33]. More radical alterations of the basic natural structure, involving the opening of ring A, have been performed. A recent study reported the 11-step total synthesis of an etoposide analog having modifications in rings A and D, Fig. (11). 

All characteristic last steps in the synthesis of EDOT, i.e. the ring closure to the dioxane structure, are also sufficient for the formation of the analogous seven-membered rings (1,3-dioxepanes), the 3,4-propylenedioxythiophenes (ProDOTs) Williamson ether synthesis [13], transetherification [30] and Mitsunobu reaction [25]. The analogous basic five-membered ring compound 3,4-methylenedioxythiophene (MDOT, a 1,3-dioxolane derivative) is also accessible by Williamson ether synthesis using bro-mochloromethane [31]. 

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See also in sourсe #XX -- [ , ]

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