Threo Isomer

Carbonyl 1,2 Asymmetric Induction - Cram's Rule
... a mixture of diastereomers, predominantly the threo isomer (see for explanation the Fischer projection) ... The preference for the formation of the threo isomer can be explained by the rule stated above by having the active nucleophile in this reaction attacking the carbonyl group from the ... in the same reaction product as above but now with preference for the erythro isomer (2a) ...