Iridium-catalyzed anti-diastereo- and enantioselective carbonyl (trimethylsilyl)allylation from the alcohol or aldehyde oxidation level.
Using the ortho-cyclometalated pi-allyl iridium precatalyst (R)-I derived from [Ir(cod)Cl](2), 4-cyano-3-nitrobenzoic acid, (R)-SEGPHOS, and allyl acetate, enantioselective transfer hydrogenation of alpha-(trimethylsilyl)allyl acetate in the presence of aldehydes 2a-i mediated by 2-propanol delivers products of (trimethylsilyl)allylation 4a-i in good isolated yields and with exceptional levels of anti-diastereoselectivity and enantioselectivity (90-99% ee). In the absence of 2-propanol, but under otherwise identical reaction conditions, carbonyl (trimethylsilyl)allylation is achieved directly from the alcohol oxidation level to furnish an equivalent set of adducts 4a-i with roughly equivalent isolated yields and stereoselectivities. To evaluate the synthetic utility of the reaction products 4a-i, adduct 4g was converted to the 1,4-ene-diol 5g via dioxirane-mediated oxidative desilylation with allylic transposition, the allylic alcohol 6g via protodesilylation with allylic transposition, and the gamma-lactam 7g via chlorosulfonyl isocyanate-mediated cycloaddition.
Han
Soo Bong
SB
Department of Chemistry and Biochemistry, University of Texas at Austin, Austin, Texas 78712, USA.
Gao
Xin
X
Krische
Michael J
MJ
D000085:Acetates / Q000737:chemistry; D000438:Alcohols / Q000737:chemistry*; D000447:Aldehydes / Q000737:chemistry*; D000498:Allyl Compounds / Q000737:chemistry; D002384:Catalysis; D007495:Iridium / Q000737:chemistry*; D009579:Nitrobenzoates / Q000737:chemistry; D010084:Oxidation-Reduction; D012825:Silicon / Q000737:chemistry; D013237:Stereoisomerism; D013379:Substrate Specificity; D014297:Trimethylsilyl Compounds / Q000737:chemistry*
D000085:Acetates; D000438:Alcohols; D000447:Aldehydes; D000498:Allyl Compounds; D009579:Nitrobenzoates; D014297:Trimethylsilyl Compounds; D007495:Iridium; C498551:allyl acetate; D012825:Silicon