Alkylthioalkyl lactones

Abstract

Compounds of the formula ##STR1## and their preparation wherein R.sup.1 and R.sup.2 are each selected from H and alkyl wherein the alkyl moieties are straight or branched chain of 1-20 carbons, preferably 1-6 carbons. Readily prepared therefrom are the corresponding unsaturated esters of the formula R.sup.2 S(R.sup.1)CH--CH.sub.2 --CH.dbd.CH--COO-alkyl which are useful as intermediates in the preparation of herbicides.

Description

This invention concerns novel alkylthioalkyl lactones and a markedly improved process for their preparation. The lactones find utility as intermediates in the preparation of herbicides.

The invention more particularly concerns the novel lactone compounds of the formula ##STR2## and their preparation wherein R.sup.1 and R.sup.2 are each selected from H and alkyl wherein the alkyl moieties are straight or branched chain of 1-20 carbons, preferably 1-6 carbons such as methyl, ethyl, propyl, isobutyl, or hexyl. Readily prepared from these lactones are the corresponding unsaturated esters of the formula R.sup.2 S(R.sup.1)CH--CH.sub.2 --CH.dbd.CH--COO--alkyl which are useful as intermediates in the preparation of herbicides according to and such as those disclosed in U.K. Pat. No. 2,090,246, incorporated herein by reference.

The present lactones are prepared by contacting an aldehyde of the formula ##STR3## with ketene at a temperature of from about 0.degree. C. to about 30.degree. C., preferably from about 15.degree. C. to about 25.degree. C., in the presence of a catalytic amount of a Lewis acid catalyst in a low-boiling ether or ester solvent.

In a specific preferred embodiment, the present invention encompasses the compound (I) of the formula ##STR4## and its manufacture, which compound is employed in the preparation of the herbicide of the formula ##STR5## sold under the tradename SELECTONE. This herbicide is prepared, for example, from the above compound (I) by the reaction sequence ##STR6##

In accordance with the present invention, ketene is reacted with the aldehyde at about 0.degree. C. to about 30.degree. C. in the presence of a catalytic amount (about 0.35 to about 35 mole % of the total moles of the aldehyde) of a Lewis acid catalyst such as BF.sub.3, BF.sub.3.Et.sub.2 O, ZnBr.sub.2, ZnI.sub.2, FeCl.sub.3, MgBr.sub.2, or the like, in a low-boiling ether or ester solvent such as diethyl ether, tetrahydrofuran, 1,4-dioxane, dipropyl ether, dibutyl ether, ethyl acetate, methyl acetate, dimethoxyethane or the like, according to the equation

The following examples will further illustrate the invention.

EXAMPLE 1

Preparation of Compound (I)

A solution of 38.6 g (0.288 mole) of distilled 3-(ethylthio)butyraldehyde and 1.5 ml of BF.sub.3.Et.sub.2 O (0.01 moles) in 350 cc of diethyl ether in a round bottom flask equipped with stirrer was stirred at 20.degree. C. on a water bath while ketene gas was added through a frit at such quantity and flow rate as to provide a controlled reaction. After about 1.5 hours, IR analysis of an aliquot showed all aldehyde to be consumed and a strong .beta.-lactone carbonyl band at 5.5.mu.. The mixture was purged with N.sub.2, washed with 25 ml of saturated aqueous NaHCO.sub.3, dried with MgSO.sub.4, stripped of ether, and distilled (Kugelrohr 75.degree.-85.degree./1 mm Hg) to give 36.0 g (72%) of .beta.-lactone as a clear liquid. Mass spectrum and elemental analysis confirmed the Compound (I) structure.

EXAMPLE 2

Preparation of Intermediate Compound (II) of the Structure ##STR8##

To a solution of 10.0 g (0.0575 mol) of Compound I in 50 ml of methanol in a round bottom flask equipped with stirrer was added 3.19 g (0.0590 mol) of sodium methoxide and the mixture stirred overnight at ambient temperature. The mixture was stripped of methanol and partitioned between ether and water. The organic phase was dried with MgSO.sub.4 and stripped of solvent to give 8.4 g (71.2%) of crude .beta.-hydroxy ester identified by mass spectrum analysis (clear syrup).

A solution of 8.4 g (0.0407 mol) of this crude alcohol in 100 ml of dry pyridine was treated at 20.degree. C. with 7.98 g (0.0420 mol) of p-toluenesulfonyl chloride and the mixture stirred at room temperature for 2.5 hours. The reaction mixture was then heated on the steam bath to about 70.degree. C. for 3 hours and let stand at room temperature overnight. The reaction mixture was poured into water, extracted with ethyl acetate, washed with 10% HCl and then with water, dried with MgSO.sub.4 and stripped of ethyl acetate. The residue was distilled in a short-path apparatus to give 5.03 g (65.6%) of the desired Compound (II) identified by mass spectrum analysis.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications will be effected within the spirit and scope of the invention.

Claims

1. A compound of the formula ##STR9## wherein R.sup.1 and R.sup.2 are each selected from H and alkyl of 1-20 carbons.

2. A compound according to claim 1 wherein R.sup.1 and R.sup.2 are each selected from alkyl of 1-6 carbons.

3. The compound according to claim 1 of the formula ##STR10##