Abstract
A concise route to macrolactone 38 ,
an advanced intermediate of the Nicolaou/Chen synthesis
of palmerolide A, is described. Key steps in our synthesis include
a Noyori transfer hydrogenation of an alkynone, chain extension
via Claisen rearrangement, and an ADH reaction on an enyne. After
reduction of the triple bond, a selective silylation served to differentiate
the hydroxy groups of the diol, which allowed for the
preparation of aldehyde 30 containing already
the carbamate function. A HWE reaction produced the substrate for
an intramolecular Heck coupling. In contrast to the Stille cyclization,
the Heck cyclization produced only the desired 14E ,16E -diene. Elaboration of the C-19 side
chain led to the key lactone 38 .
Key words
asymmetric synthesis - dihydroxylations - Heck
reaction - macrocycles - natural products
