demetalation

1,6-Enynes such as 1q react with aromatic aldehydes in a formal [2 + 2 + 2] cycloaddition to give oxabicyclic adducts of type 55 together with dienes 56, which result from a metathesis-type reaction of the enyne with the aldehyde (Scheme 16 ). 95 The formation of these products can be explained by attack of the aldehyde to the cyclopropyl gold carbene intermediate to form 53a, which undergoes a Prins-type cyclization followed by either demetalation to form 55 or fragmentation to give 56 .