Alkoxy trans-products formation

The initial transmetalation of 249 leads to 250 via anti-SE substitution and additional isomerizations provide 251 and 252. The closed, six-membered transition state 253 from 250 is used to rationalize formation of the E-anti-alcohol 254 as the major product, whereas the minor -xyn-adduct 256 is generated from 252 via the closed arrangement 255. The stereochemical consequences for InCh trans-metalations are complimentary to the syn outcome of reactions for y-(alkoxy)allylstannanes. As a result, the technique has been utilized in organic synthesis, with the illustration of several applications in Scheme 5.2.56. ... 

When TiCU is used as a catalyst with substituted dienes such as (14), a predominant route is the Mu-kaiyama aldol process, " When diene (14) reacts with benzaldehyde the trans (anti) product is observed. When compound (42) is used as the aldehyde, one observes exclusive formation of the (erythro) aldol products (Table 14). These stereochemical results can be rationalized by using a Zimmerman-Traxler transition state (Scheme 18). Chelation by the metal of the aldehyde a-alkoxy group causes it to be placed in a pseudo axial position in the transition state structure. This results in a stereochemical relationship that gives syn aldol products. ... 

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