A convergent synthetic approach is outlined to the tricyclic compound I& which contains the full carbon skeleton of olivin.
Olivin (A) is the aglycone of the olivomycin group of antitumor antibiotics.
2 These compounds, along with the structurally related chromomycins 3 and mithramycins, 4 are currently being evaluated in the clinic5 as cancer chemotherapy agents. We recently described a synthetic approach to the tricyclic nucleus of olivin. 6 However, our synthesis was rather long, and thus we have recently concentrated on developing a shorter, more convergent route to the olivin skeleton. In this note we describe an efficient synthesis of tricyclic compound &which contains the complete carbon framework and much of the functionality of olivin (A).
Our starting material was dithiolane A, which was prepared in 77% yield from 3,5-dimethoxybenzaldehyde on treatment with 1,3-propanedithiol in CHC13 saturated with dry Xl7 (mp 94-95'C).
Acylation of the anion derived froma (n-butyl lithium, THF, -20Β°) with readily available ester 3_N at -78" gave the ketoneA (63% based on 2; IR (film) 1720 cm-'). Sodium borohydride reduction of thisketone(EtOH, room temp, 24 hr) gave alcoholA(99%, as a 70:30 mixture of