The enantiomerically pure C(2)-symmetrical hexa-1,5-diene-3,4-diol is selectively monopropargylated. The products undergo ring-closing enyne metathesis to give exclusively dihydropyrans as single stereoisomers. An unprotected hydroxy group is identified as the factor controlling the ring-size selectivity.

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SummaryThe catalytic performance of NHC-ligated Ru-indenylidene or benzylidene complexes bearing a tricyclohexylphosphine or a pyridine ligand in ring closing metathesis (RCM), cross metathesis, and ring closing enyne metathesis (RCEYM) reactions is compared. While the PCy3 complexes perform significantly better in RCM and RCEYM reactions than the pyridine complex, all catalysts show similar activity in cross metathesis reactions.

A protected derivative of (3R,4R)-hexa-1,5-diene-3,4-diol, a conveniently accessible C 2 -symmetric building block, undergoes single or double cross metathesis with methyl acryl-

A sequence of selective monoprotection and Rh-catalyzed enantioconservative allylic substitution is established as a desymmetrization strategy for C(2)-symmetric hexa-1,5-diene-3,4-diol. A benzyl protecting group and ethyl carbonate as a leaving group emerged as the most useful combination with respect to reproducibility, stereoselectivity, and yield. A remarkable deviation from the normally observed regiospecificity of Rh-catalyzed allylic alkylations was observed for unprotected carbonates. In this case, a linear, rather than a branched alkylation product was obtained exclusively.