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Formal [4+2] cycloaddition of di-tert-butyl 2-ethoxycyclobutane-1,1-dicarboxylate with ketones or aldehydes and tandem lactonization.

Chemical & pharmaceutical bulletin (2012-01-10)
Ryohei Okado, Aya Nowaki, Jun-Ichi Matsuo, Hiroyuki Ishibashi
ABSTRACT

A catalytic amount of tin(IV) chloride catalyzed formal [4+2] cycloaddition reaction of di-tert-butyl 2-ethoxycyclobutane-1,1-carboxylate with ketones or aldehydes to give diethyl 6-ethoxydihydro-2H-pyran-3,3(4H)-dicarboxylates, whereas two equivalents of trimethylsilyl triflate promoted tandem [4+2] cycloaddition and lactonization to afford 3-oxo-2,6-dioxabicyclo[2.2.2]octane-4-carboxylate esters.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
Tin(II) chloride, reagent grade, 98%
Sigma-Aldrich
Tin(II) chloride dihydrate, ACS reagent, 98%
Sigma-Aldrich
Tin(II) chloride dihydrate, reagent grade, 98%
Sigma-Aldrich
Tin(II) chloride dihydrate, ≥99.995% trace metals basis
Sigma-Aldrich
Tin(II) chloride, anhydrous, powder, ≥99.99% trace metals basis
Sigma-Aldrich
Tin(II) chloride dihydrate, puriss. p.a., ACS reagent, reag. ISO, reag. Ph. Eur., ≥98%
Sigma-Aldrich
Tin(II) chloride, ≥99.99% trace metals basis
Supelco
Tin(II) chloride dihydrate, suitable for AAS
Sigma-Aldrich
Tin(II) chloride dihydrate, ≥99.99% trace metals basis