Alkynoate Synthesis through the Vinylogous Reactivity of Rhodium(II) Carbenoids

Abstract

A new rhodium carbenoid approach to access alkynoates has been developed. This transformation combines the addition of enol ethers at the vinylogous position of β-siloxy-substituted vinyldiazo derivatives and an unprecedented siloxy group migration to yield the products as single diastereomers.

Rh2(R-TPCP)4-Catalyzed Enantioselective [3+2]-Cycloaddition between Nitrones and Vinyldiazoacetates

“…5 Other factors found to favor vinylogous reactivity were electron deficient dirhodium catalysts, polar solvents, and bulky esters on the carbenoid. Recently, we 6 and others 7 have studied this unusual vinylogous reactivity in a variety of transformations, using a combination of experimental and theoretical studies to gain a better understanding of this chemistry. 8 We have found that dimolybdenum, diruthenium and especially silver catalysts enhance vinylogous reactivity.…”

“…8 We have found that dimolybdenum, diruthenium and especially silver catalysts enhance vinylogous reactivity. 6a-c Another major breakthrough was the discovery that chiral bulky dirhodium catalysts could enhance vinylogous reactivity, especially if the trapping nucleophile is also sterically demanding. 6d …”

Silver-Catalyzed Vinylogous Fluorination of Vinyl Diazoacetates

“…3 Traditional approaches for the synthesis of γ-fluoro-α,β-unsaturated carbonyls mainly rely on electrophilic fluorination of conjugated enol ethers 4 and Wittig-type reaction of α-fluoro aldehydes or ketones. 5 Recently, we 6 and others 7 have described that metal-stablized vinylcarbenes derived from vinyldiazoacetates can selectively display electrophilic reactivity at the vinylogous position instead of the carbene site. This type of behavior is especially favorable when silver catalysts are used.…”

“…This type of behavior is especially favorable when silver catalysts are used. 6c,6d,7h In this communication, we report a silver-catalyzed vinylogous fluorination to generate highly functionalized γ-fluoro-α,β-unsaturated carbonyls (eq. 1).…”

“…A similar selectivity has been seen in vinylogous hydroxylation of steroidal diazo via silver catalysis and has been rationalized to be due to stereoelectronic effects from the conformation of the steroid used. 6e …”