Traceless Protection for More Broadly Applicable Olefin Metathesis

An operationally simple in situ protection/deprotection strategy that significantly expands the scope of kinetically controlled catalytic Z‐ and E‐selective olefin metathesis is introduced. We demonstrate that, prior to the addition of a sensitive Mo‐ or Ru‐based complex, treatment of a hydroxy‐ or a carboxylic acid‐containing olefin with commercially available HB(pin) or readily accessible HB(trip)2 (pin = pinacolato, trip = 2,4,6‐tri(iso‐propyl)phenyl) for 15 minutes is sufficient for efficient generation of a desired product. Routine workup leads to quantitative deprotection. A range of stereochemically defined Z‐ or E‐alkenyl chlorides, bromides, fluorides, and boronates or Z‐trifluoromethyl‐substituted alkenes with a hydroxy‐ or a carboxylic acid group were thus prepared in 51–97% yield and 93% to >98% stereoselectivity. The substrates, HB(pin), and cross‐partners were used as received. We also show that, regardless of whether a polar functional unit is present or not, a small amount of HB(pin) (e.g., 10 mol %) may be used to remove residual water, significantly enhancing efficiency (i.e., lower catalyst loading).

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