  We present the spectra of Complex Organic Molecules (COMs) detected in HOPS
373SW with the Atacama Large Millimeter/submillimeter Array (ALMA). HOPS 373SW,
which is a component of a protostellar binary with a separation of 1500 au, has
been discovered as a variable protostar by the JCMT Transient monitoring survey
with a modest ~30% brightness increase at submillimeter wavelengths. Our ALMA
Target of Opportunity (ToO) observation at ~345 GHz for HOPS 373SW revealed
extremely young chemical characteristics with strong deuteration of methanol.
The dust continuum opacity is very high toward the source center, obscuring
line emission from within 0.03 arcsec. The other binary component, HOPS 373NE,
was detected only in C17O in our observation, implying a cold and quiescent
environment. We compare the COMs abundances relative to CH3OH in HOPS 373SW
with those of V883 Ori, which is an eruptive disk object, as well as other hot
corinos, to demonstrate the chemical evolution from envelope to disk. High
abundances of singly, doubly, and triply deuterated methanol (CH2DOH, CHD2OH,
and CD3OH) and a low CH3CN abundance in HOPS 373SW compared to other hot
corinos suggest a very early evolutionary stage of HOPS 373SW in the hot corino
phase. Since the COMs detected in HOPS 373SW would have been sublimated very
recently from grain surfaces, HOPS 373SW is a promising place to study the
surface chemistry of COMs in the cold prestellar phase, before sublimation.
