“…Dimethoxycarbene ( 6 ), generated in situ by thermal decomposition of 2,2-dimethoxy-2,5-dihydro-1,3,4-oxadiazole 7 , reacts with E - 1b yielding a mixture of the trans -configured tetramethoxycyclobutane 8 and 2,3-dihydrofuran 9 [ 21 – 22 ] ( Scheme 3 ). The latter reacts further with dimethoxycarbene and converts into the orthoester 10 via insertion into the C–O bond.…”