l‐Menthol‐Assisted Synthesis of P‐Stereogenic Phosphinous Acid Amides and Phosphine‐Boranes

Abstract

Diastereomerically pure phenylphosphonous acid‐borane l‐menthyl ester N,N‐diethylamide was obtained through the fractional crystallization of a diastereomeric mixture of compounds synthesized from PhPCl2, l‐menthol, diethylamine, and BH3·THF. Treatment of racemic or diastereomerically pure phenylphosphonous acid‐borane derivatives with sodium in liquid ammonia followed by the addition of an electrophile led to the formation of phosphinous acid‐amides. Surprisingly, these compounds undergo preferential P–N bond cleavage under Birch reduction conditions.

Prolinol as a Chiral Auxiliary in Organophosphorus Chemistry

“…(Scheme 8) Also, reactions of tricoordinated oxazaphospholidine with organometallic reagent such as methyl lithium and methyl magnesium bromide afforded the same effects. Replacement of alkoxy group by an alkyl group can be also accomplished via a sequence of PÀ O bond cleavage with alkali metals in liquid ammonia [12] followed by an alkylation with an alkyl halide. The same set of substrates was therefore submitted to a reaction with lithium in liquid ammonia followed by a reaction with methyl iodide as an electrophile (Scheme 9, Table 5).…”

“…These results are quite interesting as usually a cleavage of PÀ O bond proceeds with high degree of stereospecificity. [12,13] It is difficult to conclude now, what is the reason of such a behavior as the structure of the substrate seems to lack any special interactions in the molecule.…”

A Powerful P−N Connection: Preparative Approaches, Reactivity, and Applications of P‐Stereogenic Aminophosphines

“… Synthesis towards diastereomerically pure (−)‐menthol‐substituted aminophosphine borane [(1 R C ,2 S C ,5 R C , R P )‐ 29 ], which can be substituted by a methyl and a methoxy entity while maintaining the stereochemical integrity at the phosphorus center (DCM=dichloromethane) [35] …”

“…The absolute configurations of all products were derived from literature precedents. [35] Besides monodentate N-and O-bound chiral auxiliaries, also bidentate auxiliaries are part of the synthesis repertoire for providing P-stereogenic compounds. A prominent example is (À )-ephedrine [(1R C ,2S C )-32], which was introduced by Inch [37] (Scheme 6) in the 1970s and further studied by Jugé (Scheme 7) around the turn of the millenium.…”

Functional Phosphine Derivatives Having Stationary and Flexible Chiralities: Their Preparation and Chirality Controlling

“…Chiral tertiary phosphines (CTPs) are widely applied in asymmetric catalysis as ligands of metallic catalysts and as organocatalysts, which contain either chiral carbon skeleton or stereogenic phosphorus atom. − The CTPs, even for that have sole chirality, are usually acquired from multistep conversions or via tedious kinetic resolutions . A chiral auxiliary is usually employed for the preparation of P- stereogenic CTPs, via alkylating, cross-coupling, addition, and substitution. − The lengthy synthesis route probably results in chirality loss so that the reactions are usually performed under harsh conditions such as low temperature or strong alkali reagents…”