Chemoenzymic preparation of asymmetrized tris(hydroxymethyl)methane (THYM*) and of asymmetrized bis(hydroxymethyl)acetaldehyde (BHYMA*) as new highly versatile chiral building blocks
摘要:
A series of asymmetrized tris(hydroxymethyl)methanes 2 and bis(hydroxymethyl)acetaldehydes 3 have been prepared in both enantiomeric forms through a chemoenzymatic methodology. The key step is the highly enantioselective PPL-catalyzed monohydrolysis of 2(E)-alkenyl-1,3-diacetoxypropanes 25-27. A careful study on the effect of unsaturations adjacent to the prochiral center in a series of 2-substituted 1,3-diacetoxypropanes has confirmed the suggested beneficial effect of a pi-system in that position but has also unveiled an unprecedented dramatic effect of double-bond configuration on enantioselectivity. A new empirical model for the interpretation of these and other results, based both on polarity and steric arguments, is proposed. This study provides a general protocol for the efficient synthesis of asymmetrized 1,3-propanediols bearing in position 2 saturated or unsaturated carbon chains.
Protecting group controlled diastereoselective allylation of asymmetrized bis (hydroxymethyl)acetaldehydes (BHYMA*)
作者:Giuseppe Guanti、Luca Banfi、Enrica Narisano
DOI:10.1016/0040-4039(91)80449-g
日期:1991.11
MgBr2 catalysed allylation of a series of diprotected asymmetrized bis (hydroxymethyl)acetaldehydes 2 with allyltributylstannane proceeds with good diastereoselectivity. The stereochemical results are in line with a cyclic chelated transition state, where only one of the two CH2OR appendages, due to the different nature of protecting groups, is capable of coordinating the Lewis acid.