The reaction of carboxylate-stabilised sulfur ylides (thetin salts) with aldehydes and ketones has been investigated. Using both achiral and chiral sulfur ylides, good yields were obtained with dimsylsodium or LHMDS as bases in DMSO or THF–DMSO mixtures. However, the enantioselectivities observed with a camphor-based sulfide were only moderate (up to 67%). The reaction was studied mechanistically by independent generation of the betaine ...