Exploring Border Conditions for Spontaneous Emergence of Chirality in Allylboration of 1,2,3-Triazolic Aldehydes.

A case of spontaneous chirality generation was observed during a synthetic project studying the allylboration of 1,2,3-triazolic aldehydes. Here, we present computational studies supported by experimental findings targeting the elucidation of border conditions required for the observation of spontaneous chirality generation in the reaction of 1-Ar-1-1,2,3-triazole-4-carbaldehydes with triallylborane. Three possible sources of symmetry breaking were found computationally. Thus, dimerization of the initial reaction products, alcoholates , gives dimers (homochiral) and (heterochiral). The latter were computed to be more stable thermodynamically, which can lead to amplification of the initial stochastic imbalance of the enantiomers of via the reservoir mechanism. Furthermore, enantiomeric excess can be increased during the transfer of the second allylic group in the reaction of optically active boronates with , which was computed to be enantioselective due to the strong activating and stereoregulating properties of the 1,2,3-triazole group. In addition, reactions of borinic esters , products of the previous reaction with triallylborane, recovered in each case two molecules of of the same handedness, which can lead to additional chirality amplification. Experimentally, reactions of optically active alcohols (+)-- with triallylborane provided chiral alcoholates which were reacted with equivalent amounts of corresponding aldehydes . Unexpectedly, in two series of 10 experiments each, preferential formation of both enantiomers of the newly formed product was observed: seven times and three times in the case of and six times and four times in the case of .