6jt Electrocyclic ring closure

It is assumed that first biradical 5-63 is formed on addition of 5-62 to photochemi-caUy excited 5-61. There follows a ring closure involving the triple bond to yield a-acyl-a, (5-uri saturated carbene 5-64. The carbene moiety then undergoes a final 6jt electrocyclic ring closure on the carbonyl group to give the desired furan 5-65. 

A-aryl ketenimines, substituted at the ort/io-position either with noncyclic acetalic functions, undergo thermal rearrangement to 3,4-dihydroquinolines involving 1,5 hydride or alkoxy migration followed by subsequent 6jt electrocyclic ring closure (Scheme 65)7 ... 

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