We present high angular resolution 1.1mm continuum and spectroscopic ALMA observations of the well-known massive proto-cluster Mon R 2 IRS 3.The continuum image at 1.1mm shows two components, IRS 3 A and IRS 3 B, that are separated by $sim$0.65$$. We estimate that IRS 3 A is responsible of $sim$80 % of the continuum flux, being the most massive component. We explore the chemistry of IRS 3 A based on the spectroscopic observations. In particular, we have detected intense lines of S-bearing species such as SO, SO$_2$, H$_2$CS and OCS, and of the Complex Organic Molecules (COMs) methyl formate (CH$_3$OCHO) and dimethyl ether (CH$_3$OCH$_3$). The integrated intensity maps of most species show a compact clump centered on IRS 3 A, except the emission of the COMs that is more intense towards the near-IR nebula located to the south of IRS 3 A, and HC$_3$N whose emission peak is located $sim$0.5$$ NE from IRS 3 A. The kinematical study suggests that the molecular emission is mainly coming from a rotating ring and/or an unresolved disk. Additional components are traced by the ro-vibrational HCN $ u_2$=1 3$rightarrow$2 line which is probing the inner disk/jet region, and the weak lines of CH$_3$OCHO, more likely arising from the walls of the cavity excavated by the molecular outflow. Based on SO$_2$ we derive a gas kinetic temperature of T$_k$$sim$ 170 K towards the IRS 3 A. The most abundant S-bearing species is SO$_2$ with an abundance of $sim$ 1.3$times$10$^{-7}$, and $chi$(SO/SO$_2$) $sim$ 0.29. Assuming the solar abundance, SO$_2$ accounts for $sim$1 % of the sulphur budget.
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