The asymmetric Maitland-Japp reaction and its application to the construction of the C1-C19 bis-pyran unit of phorboxazole B.

The synthesis of the C1-C19 bis-pyran unit of phorboxazole B has been achieved. The key pyran rings were constructed by means of an asymmetric Maitland-Japp reaction and a second Maitland-Japp resolution/cyclization reaction. The longest linear sequence was 14 steps, and the C1-C19 bis-pyran unit was formed in an impressive 10.4% yield.