Boron imide, condensed derivatives

Boron halides, coordination compounds with amines, 5 26 Boron imide, condensed derivatives of, from boron halide-amine coordination compounds, 6 28 Boron oxide, porous, 2 22 Bromamide, di- (NHBr2), 1 62 analysis of, 1 64... 

These two compounds are among the thermally more stable boron halide-amine compounds. Compounds derived from certain primary and secondary amines lose hydrogen halides at elevated temperatures to give condensed boron-imide or borazole (borazine) derivatives. 

A key step in the synthesis of the spiroketal subunit is the convergent union of intermediates 8 and 9 through an Evans asymmetric aldol reaction (see Scheme 2). Coupling of aldehyde 9 with the boron enolate derived from imide 8 through an asymmetric aldol condensation is followed by transamination with an excess of aluminum amide reagent to afford intermediate 38 in an overall yield of 85 % (see Scheme 7). During the course of the asymmetric aldol condensation... 

The synthesis of the polyol glycoside subunit 7 commences with an asymmetric aldol condensation between the boron enolate derived from imide 21 and a-(benzyloxy)acetaldehyde (24) to give syn adduct 39 in 87 % yield and in greater than 99 % diastereomeric purity (see Scheme 8a). Treatment of the Weinreb amide,20 derived in one step through transamination of 39, with 2-lithiopropene furnishes enone 23 in an overall yield of 92 %. To accomplish the formation of the syn 1,3-diol, enone 23 is reduced in a chemo- and... 

Similarly, condensation of the disaccharide derivative (404) [125] via the imidate (405) with the trisaccharide (392) in the presence of boron trifluoride — etherate gave a pentasaccharide in 40 % yield and this was converted into the imidate (403), using the same techniques as described for the preparation of (402). Condensation (33 % yield) of the imidate (403) with a 3-O-benzoylceramide (63) and deprotection of the product gave the ganglioside GMI (401). 

Other uses of oxazinone enolates have been described by Williams, including the boron enolate 60, in the synthesis of diaminopimelic acid (62), the penultimate precursor of the essential amino acid i.-lysine (Scheme 10.8) [59], Acylated derivatives of Oppolzer s camphor sultam 63 can readily be alkylated in a highly diastereoselective fashion (Scheme 10.9) [60]. Thus, the imide derived from the condensation of 63 and 64 undergoes enolization and subsequent alkylation to furnish protected amino acid derivatives with high selectivity (cf 65, dr > 99 1) [61],... 

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