to the larger size of the tributylstannyl group compared to the tert-butyl group.
Another reason for the enhancement of the reactivity of the diene can also be a
stereoelectronic effect due to the interaction between Sn and O atoms or the Sn
atom and the Ru carbene complex.
A simple stereoselective synthesis of cis- and trans-2,3-disubstituted mediumsized cyclic ethers 59 and 61 (Scheme 10) has been developed [30] based on the
Ireland–Claisen rearrangement and RCM. The glycolate ester 57 was prepared by a
condensation of glycolic acid 56 with (E)-3-benzyloxy-2-propenol 55.
Deprotonation of 57 with KHMDS at À78
C for 5 min followed by treatment
with TMSCl and warming to rt induced an Ireland–Claisen rearrangement and, after
esterification with diazomethane ester 58, was isolated in 79 % overall yield. The
RCM using the first-generation Grubbs catalyst 9 provided the eight-membered
Scheme 8 Effect of the relative stereochemistry of the substituents
Scheme 9 Effect of tributylstannyl group on the conformation in RCM
Scheme 10 Claisen–Ireland rearrangement and RCM
330
E. Soriano and J. Marco-Contelles
Another reason for the enhancement of the reactivity of the diene can also be a
stereoelectronic effect due to the interaction between Sn and O atoms or the Sn
atom and the Ru carbene complex.
A simple stereoselective synthesis of cis- and trans-2,3-disubstituted mediumsized cyclic ethers 59 and 61 (Scheme 10) has been developed [30] based on the
Ireland–Claisen rearrangement and RCM. The glycolate ester 57 was prepared by a
condensation of glycolic acid 56 with (E)-3-benzyloxy-2-propenol 55.
Deprotonation of 57 with KHMDS at À78
C for 5 min followed by treatment
with TMSCl and warming to rt induced an Ireland–Claisen rearrangement and, after
esterification with diazomethane ester 58, was isolated in 79 % overall yield. The
RCM using the first-generation Grubbs catalyst 9 provided the eight-membered
Scheme 8 Effect of the relative stereochemistry of the substituents
Scheme 9 Effect of tributylstannyl group on the conformation in RCM
Scheme 10 Claisen–Ireland rearrangement and RCM
330
E. Soriano and J. Marco-Contelles