Insertions of silylated carbenoids into vinylzirconocene chlorides. A convergent route to silyl-substituted allylzirconium reagents

Kasatkin, Alexander N.; Whitby, Richard J.

doi:10.1016/s0040-4039(99)01982-6

Cited by 21 publications

(1 citation statement)

References 32 publications

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“…Our recent efforts in this area have focused on the stereoselective construction of multistereogenic centers including a quaternary carbon by the reaction of allyltitanium species with ketones . Similar steric discrimination of a carbonyl based strategy for the construction of adjacent stereocenters has also been examined using organoboron, tin, silicon, zinc, zirconium, aluminum, and samarium species. However, in most of these reactions, high diastereoselectivity is observed only when aldehydes and highly sterically crowded alkyl methyl ketones are employed.…”

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Diastereoselective Addition of Allyltitanocenes to Cyclic Enones

et al. 2012

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Diastereoselective Addition of Allyltitanocenes to Cyclic Enones

et al. 2012

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Hydrozirconation of Alkynes

Milligan,

Hammill,

Crocker

et al. 2023

Organic Reactions

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Since the first preparation of organozirconocenes from alkenes and alkynes in 1972, hydrozirconation has become one of the most commonly used stoichiometric methods to convert readily available starting materials into reactive but stable organometallic intermediates. A broad range of subsequent transformations may be employed to convert organozirconocenes in situ into high‐value functionalized products, often with the strategic formation of one (or several) new carbon–carbon bonds. This chapter focuses on the hydrozirconation of terminal and internal alkynes, and the subsequent synthetic transformations of the resulting alkenylzirconocenes. Zirconocene hydrochloride, Cp 2 Zr(H)Cl, is most frequently employed for the hydrozirconation step and can be used as a reagent or prepared in situ. Subsequent reactions of alkenylzirconocenes include additions to inorganic electrophiles such as halogens, as well as in situ ligand transfers to other metals, such as palladium and zinc, that further expand the range of accessible bond formations. The initial discussion focuses on the mechanism and stereochemical considerations, and on the steric and electronic factors that determine the regiochemistry of the either kinetically or thermodynamically controlled hydrozirconation. The “Scope and Limitations” section presents information on functional group compatibilities and is organized by the type of synthetic transformation of alkenylzirconocenes. Representative applications of the hydrozirconation of alkynes are showcased in syntheses of natural products, comparisons to alternative methods for the hydrometallation of alkynes. The goal of this chapter is to demonstrate the significance of hydrozirconation in organic synthesis, including the utility of the stoichiometric zirconium organometallics obtained from alkyne substrates, and to provide inspiration for the future development of new synthetic methods and strategies.

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1-Silyl-1-boryl-2-alkenes: Reagents for Stereodivergent Allylation Leading to 4-Oxy-(E)-1-alkenylboronates and 4-Oxy-(Z)-1-alkenylsilanes

et al. 2001

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Allylmetal reagents have been widely used in organic synthesis. [1] In addition, allylic boranes [2] and silanes [3] are highly versatile owing to their wide availability, high stability, and low toxicity as well as excellent chemo-, regio-, and stereoselectivities. In sharp contrast, little attention has been paid to 1-silyl-1-boryl-2-alkenes, though such reagents can be regarded as a hybrid of allylic boranes and silanes and are attractive for the construction of stereochemically complex molecules. [4] Yamamoto, Yatagai, and Maruyama prepared atrimethylsilyl-substituted crotyl-9-BBN (9-BBN 9-borabicyclo[3.3.1]nonane) by deprotonation of crotyl-9-BBN followed by silylation with chlorotrimethylsilane. [5] Similar boronates were synthesized by Tsai and Matteson by the homologation of alkenylboronates with [chloro(trimethylsilyl)methyl]lithium. [6] Both reagents were found to allylate aldehydes [7] in a manner similar to allylic boranes. Although this methodology is effective for acyclic stereocontrol, allylation with allylic silanes and stereospecificity in boronselective allylation remained to be explored. Herein we describe the novel stereocontrolled synthesis of 1-silyl-1boryl-2-alkenes by gem-silylborylation of a-chloroallyllithi-ums and dual stereospecific allylation of aldehydes with silicon or boron functionality of the gem-silylboryl reagents.Recently, the novel gem-silylborylation reaction of 1-halo-1-lithio-1-alkenes with (dimethylphenylsilyl)(pinacolato)borane (1) was disclosed [8] and is considered to proceed via borate formation followed by 1,2-migration of a silyl group from an ate-type boron to a carbenoid carbon. We envisaged that the title gem-silylboryl reagents 2 might be prepared readily by the gem-silylborylation with 1 of vinyl-substituted carbenoids [Eq. (1)]. [9,10] Thus, we treated 1 [11] with a-chloroallyllithiums generated in situ from allylic chlorides and lithium diisopropylamide (LDA) in THF at À 98 8C. The results are summarized in Table 1. Allyl chloride was converted into 2 a in 82 % yield (Entry 1). Substituted allylic chlorides were also gemsilylborylated smoothly in good yields irrespective of the substitution pattern (Entries 2 ± 7). No trace of g-silyl-aboration by 1,4-migration of a silyl group was observed. Noteworthy is that the olefinic configuration was perfectly retained in compounds 2 (Entries 3 ± 5): stereochemically pure allylic chlorides gave single stereoisomers of 2.

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Insertions of silylated carbenoids into vinylzirconocene chlorides. A convergent route to silyl-substituted allylzirconium reagents

Cited by 21 publications

References 32 publications

Diastereoselective Addition of Allyltitanocenes to Cyclic Enones

Diastereoselective Addition of Allyltitanocenes to Cyclic Enones

Hydrozirconation of Alkynes

1-Silyl-1-boryl-2-alkenes: Reagents for Stereodivergent Allylation Leading to 4-Oxy-(E)-1-alkenylboronates and 4-Oxy-(Z)-1-alkenylsilanes

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