Boron trifluoride oxepane

In connection with a ciguatoxin synthesis, a cyclization (Equation 18) of stannane derivatives like 50 with tetrabutylammonium periodate followed by boron trifluoride etherate to give oxepanes, for example, 51, are... 

Boron trifluoride etherate promotes the fWt/a-selcctivc oxacyclization of polyepoxides derived from various acyclic terpenoid polyalkenes, including geraniol, farnesol, and geranylgeraniol, providing an efficient and stereoselective synthesis of substituted oxepanes and fused polyoxepanes. The oxacyclization transformations may mimic ringforming steps in the biosynthesis of trans-syn-trans-fused polycyclic ether marine natural products <2002JOC2515>. 

Alkynes too have found application in the synthesis of oxepanes. The A/B ring system (45) of ciguatoxin has been formed in a stereoselective manner by cyclisation of the alkyne cobalt complex (44) with boron trifluoride followed by reductive removal of the chromium with... 

Intramolecular cyclisation of the aldehyde 40 with boron trifluoride etherate gave the oxepane 41 <97JOC7439>. The stereochemistry of the product is indeptendent of whether an E or a Z alkenyl group is involved in the cyclisation, although yields are higher when the E isomer is used (79%). The bicyclooxepane 43, obtained in four steps from the epoxide 42, is readily converted into the tricyclic system 44 <97TL5853>... 

Epoxides and oxetanes possessing ether substituents in the side chain rearrange in the presence of boron trifluoride etherate to form ring enlarged cyclic ethers <94H(38)2I6S>. By the appropriate selection of side chain the method may be used to form oxepanes bearing 3-CH2-0-alkyl(or alkenyl) substituents. 

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