Enzymes in organic synthesis: remarkable influence of a π system on the enantioselectivity in PPL catalysed monohydrolysis of 2-substituted 1,3-diacetoxypropanes.
Asymmetrized trils (hydroxymethyl)methane as a highly stereodivergent chiral building block: preparation of all four stereoisomers of protected 2-hydroxymethyl-1,3-butanediol
The fragment C11-C17 of tylonolide 2 was straightforwardly and stereoselectively synthesized starting from monoacetate 5, which is a synthetic equivalent of “asymmetrized tris (hydroxymethyl)methane” 3.
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.
Chemoenzymic preparation of asymmetrized tris(hydroxymethyl)methane (THYM*) and of asymmetrized bis(hydroxymethyl)acetaldehyde (BHYMA*) as new highly versatile chiral building blocks
作者:Giuseppe Guanti、Luca Banfi、Enrica Narisano
DOI:10.1021/jo00031a039
日期:1992.2
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.