A Furan to Pyran Ring Expansion

Treatment of wortmannin with trimethylsulfoxonium ylide gave the ring expanded product 2 (R = H). The Lilly chemists considered two possible mechanisms for the formation of 2 and preferred one of them on the basis that use of the perdeuterated sulfoxonium ylide gave exclusively the deuterated product 2 (R = D). 

Suggest two mechanisms for the conversion of 1 into 2, only one of which is consistent with the observed labelling study. 

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