Diastereoselective Ring-Closing Metathesis in the Synthesis of Dihydropyrans

Abstract

An investigation into the factors influencing the diastereochemical outcome of the ring-closing metathesis based synthesis of dihydropyrans is presented in this paper. Divinyl carbinols derived from alpha-hydroxy carboxylic acid esters are elaborated to trienes with two diastereotopic vinyl moieties. Depending on the steric demand of the oxo substituent of the divinyl carbinol moiety (either unprotected OH, TBDMS, or benzyl ether) different diastereomers are preferrably formed upon ring-closing metathesis. An extension to diastereoselective double ring-closing metathesis in the formation of spirocycles has also been investigated.

Homologation of Monoterpenoids into New Sesquiterpenoids via Tandem Isomerisation/Claisen Rearrangement Reactions with Three‐Component Ruthenium Catalysts, and Ru(methallyl)2(COD) Revealed by High Throughput Screening Techniques

“…Recently, it has been shown that an indenylidene-ruthenium catalyst was able to perform ring closing metathesis (RCM), isomerisation and Claisen rearrangement, successively. [8] By contrast, in the study of in situ prepared imidazolinylidene-ruthenium catalysts for RCM of 1,6-dienes and 1,6-enynes [12 -14] we found initial results [15] showing that these catalysts did not perform RCM or cycloisomerisation of 1,7-dienyl ethers but selectively led to tandem isomerisation/ Claisen rearrangement affording g,d-unsaturated aldehydes (Scheme 1).…”

Palladium‐Catalyzed O‐Allylation of α‐Hydroxy Carbonyl Compounds

“…Optical purities were determined by HPLC using a HP-LC-1050 system equipped with a Daicel Chiralcel OD column. The following compounds were prepared according to procedures described in the literature: 10c, [45] 10d, [47] 10e, [46] 10g, [49] 10h, [56] 10i, [3] 10j, [57] Pd 2 (dba) 3 · CHCl 3 , [58] [Pd(h 3 -C 3 H 5 )Cl] 2 , [59] and [Pd(PPh 3 ) 4 ]. [58] Screening Experiments for Different Pd-Precatalysts…”

“…Spectroscopic data are identical to those reported in the literature. [3] Optical rotation compares well to the val- …”

“…Spectroscopic data are identical to those reported in the literature. [3] [a] 25 D : þ 95.38 (c 1.59, MeOH). The enantiomeric excess of 11b was determined by HPLC analysis (Daicel Chiralcel OD, eluent: heptane/2-propanol, 98 : 2, flow 0.7 mL/min, 20 8C) to be > 98% after comparison with racemic 11b.…”

“…[22,23] We have successfully used the latter method for a-hydroxy esters. [2,3,5] However, application of these conditions to aromatic a-hydroxy ketones [24] turned out to give less satisfactory results, because these substrates partially undergo an oxidative C À C bond cleavage under these conditions, resulting in the formation of allyl benzoate (8) as a by-product. For 3-hydroxypropiophenone (6) and substituted derivatives this side reaction becomes a serious limitation, as approximately 50% of the starting material are converted via this pathway (Scheme 2).…”