Selective TBS-ether deprotection in presence of TBDPS-ether in the synthesis of protectin-D1

Alcohols as TBS and TBDPS  ethers: Y. Kobayashi’s group had 2 alcohol groups in protectin-D1. One (primary) was protected as TBS (tert butyldimethylsilyl) ether and the other one (secondary)  was protected as TBDPS (tert butyldiphenyl) ether.  The TBS ether was deprotected selectively keeping the TBDPS ether intact.

Installation: not shown – but fairly simple substrates.  Standard methods would have sufficed.

Survived: H₂/Pd(Lindlar), Py.SO₃/NaClO₂/CH₂N₂

Removal: PPTS, CH₂Cl₂/EtOH, 94% yield

Reference: Tetrahedron Letters, 2011, 13, 3001-3004

There is one very interesting selective hydrogentation step towards the end of the synthesis.  In Scheme 5, intermediate 27 has two acetylinic bonds – one has two alkyl chains attached to it, while the other has a TMS group and an alkene attached to it.  Hydrogenation using Pd/BaSO₄ in ethyl acetate selectively reduced the alkyne with the two alkyl chains to the cis alkene, keeping the other acetylenic bond intact to give intermediate 28.