Stereoselective synthesis of five- and six-membered carbocycles via Matteson homologation/ring closing metathesis

Abstract

The Matteson homologation is found to be a versatile tool for the stereoselective synthesis of polyunsaturated alkyl boronic esters, which can be used for the construction of five- and six-membered carbocycles via ring-closing metathesis.

Isomerization-Free Matteson Homologations of Substituted Allylboronic Esters

“…The observation that allylboronic esters can, in principle, undergo allyl isomerization under certain conditions was reported by Brown et al, although these investigators observed this reaction by heating boronic esters in toluene for more than 24 h . Although the linear product 6 was not initially anticipated, we were still able to use it for further Matteson homologations in combination with ring-closing metathesis reactions …”

“…The observation that allylboronic esters can, in principle, undergo allyl isomerization under certain conditions was reported by Brown et al, although these investigators observed this reaction by heating boronic esters in toluene for more than 24 h. 18 Although the linear product 6 was not initially anticipated, we were still able to use it for further Matteson homologations in combination with ring-closing metathesis reactions. 19 To determine when the allyl isomerization occurred, we used nuclear magnetic resonance (NMR) to analyze the crude α-chloroboronic ester 5 formed in the reaction, which clearly indicated that the terminal double bond of compound 3 had disappeared and a (E)-configured substituted double bond had formed. The same intermediate 5 and product 6 were obtained from (E)-crotylboronic ester C (Scheme 2).…”

“…In addition to this key observation, it was also shown that the absence of ZnCl 2 did not significantly reduce the diastereoselectivity of the homologation step. When the pinanediol analogue of compound 7d was used, instead of the C 2 -symmetric DICHED auxiliary as originally described by Matteson et al, 19 chiral alcohol 9 was obtained with a dr of only 95:5 (see the Supporting Informations for details).…”