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

Abstract

a-Hydroxy carbonyl compounds undergo smooth O-allylation using allylic carbonates and Pd (0) catalysts. This method has significant advantages over other O-allylation methods as it provides a solution to several problems previously observed for this synthetic transformation.

The Tandem Ring‐Closing Metathesis–Isomerization Approach to 6‐Deoxyglycals

“…With a view to the synthesis of protected l-rhodinals, ethyl lactate (1) was first allylated with allyl ethyl carbonate catalyzed by Pd 0 . [45] This reaction proceeds without racemization, in contrast to a standard Williamson ether synthesis, and gives enantiomerically pure 2. As previously reported by us, [42] 2 can be converted to 3 by a one-pot reduction of the ester function, followed by addition of vinyl magnesium chloride.…”

Synthesis of Dihydrofurans and Dihydropyrans with Unsaturated Side Chains Based on Ring Size‐Selective Ring‐Closing Metathesis

“…Compounds 5a [24] and 5b [22] have previously been obtained via this method. Method C is a Pd-catalyzed O-allylation [39] which has proven useful in cases where a protecting group migration or rather low reactivity has to be expected. We used this method for the synthesis of 6b,c from 5a,b.…”

Synthesis of 3‐Deoxy Glycals via Tandem Metathesis Sequences and Their Use in an Intermolecular Heck Arylation

“…[47,49] Vanadiumcatalysed epoxidation of 6 was investigated in different context by us. [50] The reaction yields epoxide 7 [50] in good yield and perfect regioselectivity within short periods of time. The only drawback is a diastereomeric ratio of 2:1, which is, however, irrelevant for our purposes: in a subsequent step, the alcohol was allylated to give allyl ether 8 [50] using either a Pd-catalysed reaction or a conventional Williamson ether synthesis at 0°C.…”

“…[50] The reaction yields epoxide 7 [50] in good yield and perfect regioselectivity within short periods of time. The only drawback is a diastereomeric ratio of 2:1, which is, however, irrelevant for our purposes: in a subsequent step, the alcohol was allylated to give allyl ether 8 [50] using either a Pd-catalysed reaction or a conventional Williamson ether synthesis at 0°C. Under these basic conditions low temperatures (and consequently longer reaction times) are required to prevent undesired epoxide rearrangement reactions.…”

“…Optical purities were determined by HPLC using a HP-LC-1050 system equipped with a Daicel Chiralcel OD column. The following compounds have been prepared following procedures described in the literature: 6, [47,49] 7, [50] 8, [50] 14. …”