Nitroso-Dienophile Additions to Dendralenes: A Short Synthesis of Branched Aminosugars

The first heteroatom-based dienophile cycloadditions to cross-conjugated alkenes ([n]dendralenes) are reported. Nitroso-dienophiles undergo smooth single and double Diels–Alder additions to the parent dendralenes with orientational regio- and stereoselectivity and, notably, with reactivity that depends upon the parity of the [n]dendralene. The first crystal structure of a cross-conjugated hexaene is reported. Vasella’s nitroso-sugar reagent gives a highly enantiomerically enriched double cycloadduct with [3]dendralene. This bicyclic oxazine is successively dihydroxylated and then ring-opened to form a branched chain diamino tetrol.