Table 2.

Stereoselective synthesis of (2,3-syn-3,4-syn-4,5-syn-5,6-anti)-1-aza-7-oxabicyclo[2.2.1]heptanes.

entry	homoallylic hydroxylamine	R3CHO	yield (%)	dr	product
1	34		61	≥20:1	35
2	36		60	≥20:1	37
3	38		66	6:1a	39
4	40		61	6:1a	41
5	29		80	4:1	42

^a= minor product is epimeric at the highlighted (*) position.

Note: Initial sigmatropic rearrangement for reactions summarized in entries 1 and 2 occur in <2 h, whereas substrates depicted in entries 3 and 4 required up to 48 h. Similarly, the subsequent [3+2]annulation in entries 3 and 4 require prolonged heating in comparison to entries 1 and 2 (48 h at 120 °C vs. 12 h at 120 °C). Note: products are racemic.