B-Allenyl- and B-(γ-Trimethylsilylpropargyl)- 10-phenyl-9-borabicyclo[3.3.2]decanes:  Asymmetric Synthesis of Propargyl and α-Allenyl 3°-Carbinols from Ketones

Abstract

Simple and efficient Grignard procedures are reported for the syntheses of B-allenyl-10-(phenyl)-9-borabicyclo[3.3.2]decane (1) and its B-(gamma-trimethylsilylpropargyl) counterpart (2) in both enantiomeric forms. Both add selectively to ketones, providing propargyl- and alpha-silylallenyl 3-degree-carbinols, respectively (i.e., 6 (61-93% ee) and 9 (64-98% ee)). The air-stable boron byproduct is efficiently recovered and recycled back to either 1 or 2. The ozonolysis and bromination of 9 provide nonracemic alpha-hydroxy acids and gamma-bromopropynyl carbinols, respectively.

Diastereoselective Allylation of Carbonyl Compounds and Imines: Application to the Synthesis of Natural Products

“…The expected tertiary α-allenyl carbinols were obtained in high yields and excellent enantioselectivities for methyl ketones (Table 66). 151 Compared with aldehydes, reaction times were considerably longer for methyl ketones, ranging between 3 and 36 h at −78°C…”

Asymmetric Propargylation of Ketones Using Allenylboronates Catalyzed by Chiral Biphenols

“…2 However, few methods exist to prepare them in enantioenriched form. Chiral allenyl metal reagents have proven effective 3,4 and recently described catalytic approaches 5,6,7 are notable alternatives for accessing these chiral synthetic intermediates. As a reagent for propargylation reactions, allenylboronates are attractive starting materials due to ease of preparation and predictable reactivity patterns.…”

(+)-(1S,2S)-N-Methylpseudoephedrinyl)-(10S)-phenyl-9-borabicyclo[3.3.2]decane

“…Allenylboration. 4 Simple and efficient Grignard procedures have been reported for the syntheses of B-allenyl-10-(phenyl)-9borabicyclo[3.3.2]decane (10) in both enantiomeric forms (eq 4). The reagents add selectively to ketones providing propargyl 3 •carbinols (62-85%, 61-93% ee).…”

“…Propargylboration. 4 Grignard procedures have been reported for the efficient syntheses of B-(γ-trimethylsilylpropargyl)-10-Ph-9-borabicyclo[3.3.2]decanes (12 (12S: 910787-18-7; 12R: 910787-19-8)) in both enantiomeric forms (eq 5). Their addition to ketones provides α-silylallenyl 3 • -carbinols 13 (62-95%, 64-98% ee)).…”