Design and Implementation of an Efficient Synthetic Approach to Furanosylated Indolocarbazoles:  Total Synthesis of (+)- and (−)-K252a

The first total synthesis of the natural product (+)-K252a ( 2 ) has been achieved in 12 steps from commercially available materials, with a longest linear sequence of seven steps and an overall yield of 21%. The synthetic strategy employs novel rhodium carbenoid chemistry in the construction of both the indolocarbazole aglycon ( 4 ) and the carbohydrate moiety ( 9 ).